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FOREWORD 


HIS publication is the result of the active co-operation of architects, slate producers and 

| Ree roofing contractors, governmental departments, manufacturers of accessories 

and many individual authorities. To all of these The National Slate Association ex- 
presses ils sincere appreciation of their support and interest. 

The essence of all this information supplied to the Association and to the Structural Service 
Bureau and its consulting architect, has been incorporated in the book to the fullest extent 
possible. 

In offering this handbook on slate roofs the National Slate Association has been actuated 
by the desire to supply reliable and definite information on slate and its proper application. 
It is hoped that this publication will make for the more extensive and appropriate use of 
slate as a practical, economical and attractive roofing medium besides supplying information 
on formation and quarrying to users of this invaluable and most unique stone. 

For the further benefit of the industry and of all specifiers and users of roofing slate, recom- 
mendations concerning the arrangement and contents, which may make later editions of this 
publication of even more practical use or widen its scope, will be received with appreciation by 


NATIONAL SLATE ASSOCIATION 
791 Drexel Building 


Philadelphia, Pa. 


Each illustration in this book has been carefully selected from the large number of 
photographs available for the sole purpose of making clear some particular point in the 
teat. Vor this reason the names of the Architect, Slate Producer and Contractor have 
been omitted, but can be furnished by the Association if desired. 


First Edition This is the Second of a Series of Informative Literature on Slate and Its Uses. ““ Slate Roofs” 
J 1996 The First—‘‘Charm of Slate Floors and Walks’’— Published January, 1925. P Z 
anuary, ae Copyrighted and Printed in U.S. A. rice, $1.50 


H. T. Lindeberg, Architect 


A Picturesque Slate Roof 


DIGEST OF CONTENTS 


(For Complete Index See Page 83) 


COMPLETE AUTHORITATIVE AND PRACTICAL DATA, DRAWINGS 
AND SPECIFICATIONS ON ROOFING WITH SLATE 


Characteristics 

Color—Basic list, etc. 

American Roofing Slates 
Description, where quarried, etc. 

Grading 

Commercial Standard 

Quantity per square 

Sizes 

Thickness 

Weight 

Nail holes 


SAS TEN OMe ALC Mey che acts We Ys ip soa, f wgin crs se eon ee 14 


Standard Details, Drawings and Descriptions 
Lap and Exposure 
Ridges 
Hips 
Valleys 
Eaves and Gables 
Less expensive methods of slating 


Roofing Felt: 
Recommended weights 
Laying 

Elastic Cement: 

Where to use 

Nails: 


Recommended grades, sizes, etc. 
Tables of lengths and gauges 


Tel ae latin sme rc ie che secre we a Valsiaue s wis 8 Din 


Materials described and essential data and tables 
Sizes, gauges 

Complete detail drawings 

Rule for estimating, etc. 


RooteConstrictlonest eee eae ee 34 


Handy Rafter Tables for determining size of rafter 
for given spans and spacings 


Gonstenction: Detallaye ise oe eee ce en eee ee ae 40 


Sheathing or Roof Boards 
Round Valley Foundation 
Fireproof Construction 


Geénetall Datacenter eee Pees tart 42 


Roof Slope, diagram and text 

Eaves Troughs, Gutters and Conductor Pipes 
Simplified Sizes and Weights 

Snow Guards 

Roofs and their Parts 

Piling Slate 

Estimating Slate Quantities and Costs 


SLandardespecliicationemmmm te sere. My ei een de. 48 


Complete and Short Forms 
M—Metal Work 
S—Standard Slate Roof 
T—Textural Slate Roof 
G—Graduated Slate Roof 
Flat Slate Roofs 
Specificational data on successful installations 


Reroofing with Slate 


Recommended Practice and Suggestions 


Generals Datavomolate seis ete cs ee oss 71 


History and Origin 

Geological and Chemical Formation 
Tables Mineral Constituents various slates 
Quarrying 


Possibilities in the Use of Slate 
By Albert Kelsey, F.A.LA. 


Pencil Sketches and Descriptions 


Index 


HE practical purpose of any roof is to protect the interior, the contents and the occu- 
pants of a building from rain, snow, heat and cold. In addition to these practical con- 
siderations, the roof should add to the appearance and character of the building, and 


the passing of time should only enhance its beauty and add to its intrinsic value. 


The period of usefulness of the roof will depend upon the resistance of the roofing material itself 
and the materials with which it.is laid to the action of the elements. To be permanent, the roofing 
material must be unaffected by the action of water, climatic changes and gaseous fumes in the air, 
and must also be fireproof. For economy, it should require no other material to preserve it. How- 
ever, even though the material possesses these characteristics, a permanent roof will not be secured 


unless it ts properly laid and its fastenings are selected for the same enduring qualities. 


The permanent and fireproof qualities of slate make it eminently suitable for either sloping or flat 
roofs. In no other roofing material will be found so many characteristics combining to offer such an 


alluring and indefinable variety in color, texture and line. 


This is easily understood when it is recalled that slate is a stone, formed by nature to serve the diver- 
sified uses of man. It requires no admixture of materials, domestic or foreign; it needs no heat to 
form it and no process to manufacture it other than the handiwork of extracting it from the ground in 
blocks, splitting and trimming them to the desired size and thickness. Moreover, the first cost of slate 
is not as great as that of many fabricated products, and with its practically negligible maintenance, it 
becomes the least expensive roof covering available when service and appearance are taken into ac- 
count. Besides annual savings in insurance rates most slates when removed from old roofs with care 


are as good as new. 


NATIONAL SLATE ASSOCIATION. 


SLATE ROOFS 


A Handbook of Data on the Constructing and Laying 
of All Types of Slate Roofs 


Slate roofs, the natural stone coverings, may be con- 
veniently classified as: 


Standard Slate Roofs. 
Textural Slate Roofs. 
Graduated Slate Roofs. 
Flat Slate Roofs. 


The following briefly describes each type of roof. More 
detailed information and a specification for each will be 
found on pages 48 to 65. 


Standard Roofs 


Standard slate roofs are those composed of slate ap- 
proximately 3/16” thick (Commercial Standard Slate), 
of one uniform standard length and width, having 
square tails or butts laid to a line. Slate of this type 
is commonly obtainable in the basic slate colors. Stand- 
ard roofs are suitable for any building where a perma- 
nent roofing material is desired at a minimum cost. It 
differs from other slate roofs only in characteristics af- 
fecting the texture or appearance of the roof, through the 
shape and thickness of the individual units. If desired, 
the butts or corners may be trimmed to give a hexagonal, 
diamond or “Gothic” pattern for all or part of the roof, 


Figure 1. Standard Roof 


Figure 2. Textural Roof 


as, for instance, on a church spire. Standard Roofs are 
sometimes varied by laying two or more sizes (lengths 
and widths) of Commercial Standard Slate on the same 
area. For specification see page 52. 


Textural Roofs 


The term “Textural” is used to designate those slates | 
usually of rougher texture than the Standard, with un- 
even tails or butts and with variations of thickness or 
size. In general, this term is not applied to slate over 
38” in thickness. Varying shades are frequently used to 
enhance the color effect, which, with the characteristics 
just mentioned, add interest in line and texture to the 
roof design. In addition to the basic colors of the com- 
mercial grades, accidental colorings of bronze, orange, 
etc., may also be used in limited quantities. For speci- 
fication see page 55. 


Graduated Roofs 


The graduated roof combines the artistic features of 
the Textural Slate roof with additional variations in 
thickness, size and exposure. The slates are so arranged 


Silk Lee eR eOsOur es 
ey eee ee eka as 


on the roof that the thickest and longest occur at the 
eaves and gradually diminish in size and thickness until 
the ridges are reached. Slates for roofs of this type can 
be obtained in any combination of thicknesses from 3/16” 
to 114” and heavier when especially desired. 

The graduated slate roof presents many opportunities 
for variation and offers excellent possibilities for inter- 
esting treatment. The fact that it is especially designed 
to harmonize with the general character of the building 
of which it becomes a part or to meet exacting require- 
ments of construction causes it to be frequently termed 
the custom-made roof of the industry. Many producers 
and distributors maintain special design staffs to assist 
architects in securing the most suitable and satisfactory 
graduated slate roofs. These services are freely offered 


Figure 3. Graduated Roof 


to designers in the interest of better and more harmonious 
slate roofs. For specification see page 58. 


Flat Roofs 


Flat roofs offer a wide field for roofing slate, and are 
so designated whether or not they are used for “prom- 
enade” purposes. 


Slates of any thickness may be used in place of the 
slag or gravel as a surfacing material for the usual 
built-up type of roof. The body, weight and enduring 
qualities of slate make it highly desirable as a protection 
to the waterproofing beneath the surface, whether or not 
it is subject to traffic. Only the thicker slates are used on 
promenades. [or specificational data see page 62. 


Figure 4. Flat Roof 


SLATE 


Characteristics 


The principal difference between slate and other stones 
is the natural slaty cleavage of the former, which per- 
mits it to be more easily split in one direction than in 
others. A second direction of fracture or “scallop,” 
usually at right angles to the slaty cleavage, is called the 
“srain.” Roofing slates are commonly split so that the 
length of the slate runs with the grain. 


Slate quarried for roofing stock is of dense, sound 
rock, exceedingly tough and durable. Slate, like any 
other stone, becomes harder and tougher upon exposure 
than when first quarried. It is practically non-absorp- 
tive, tests on Pennsylvania slate showing a porosity of 
0.15 to 0.4 percent. 


The nature of the surface after splitting is dependent 
upon the character of the rock from which it is quarried. 
Many slates split to a smooth, practically even and uni- 
form surface, while others are somewhat rough and un- 
even. As a result, a wide range of surface effects is 
available for the finished roof. 

Slate from certain localities contains comparatively 
narrow bands of rock differing to various degrees in 
chemical composition and color from the main body of 
the stone. These bands are called “ribbons.” Ribbons 
containing no injurious constituents and not of unde- 
sirable color are not objectionable. Slates of this type, 
when trimmed so that the ribbons are eliminated, are 
known as “clear slate.” Slates which contain sound rib- 
bons are sold as “ribbon stock.” 


NAS ele On NE Ag 


See AD elie wore: OL Cal Ame TOON 


Color 


The color of slate is determined by its chemical and 
mineralogical composition. Since these factors differ in 
various localities, it is possible to obtain roofing slates 
in a variety of colors and shades. 


It is truly remarkable to find a natural product pos- 
sessing, in addition to the other qualities before men- 
tioned, such unlimited possibilities in color effect. The 
use of slate for roofing makes it possible to obtain a 
surface of uniform or contrasting colors in cold or warm 
values. Moreover, if the design of the building requires 
a roof of one general color, it may be graded up or down 
the slope from dark to light as desired. 


Figure 5. Skulping Large Slate Slab 


To relieve the monotony of a flat uniform body color, 
various shades of the same color may be used to pro- 
vide an interesting variation up and down or across the 
roof or interspersed throughout. A low-eaved, promi- 
nent roof surface may require a quiet or contrasted blend- 
ing of the autumnal colors of nature to cause the structure 
to take its place in its intimate surroundings. Slate not 
only permits a roof of permanent color, but by the selec- 
tion of “weathering” slate, one may take advantage of 
the mellowing effect of age and weather. These and 
all the steps between these extremes are ever ready at the 
designer’s bidding in the field of slate. 


Upon exposure to the weather, all slate is changed 
slightly in color. The extent of this color change varies 
with different slate beds, being barely perceptible in 
certain slates. Those slates in which the color changes 
but slightly are classed as “permanent” or “unfading.” 
Those in which the final result is more marked and varied 
are known as “weathering” slates. 


Weathering is the natural result of exposure to the 
weather of the coloring minerals in the slate. Where 
color is an essential consideration, architects and owners 
should take this characteristic into account. The quarry 
operators know from experience the probable nature and 
extent of the changes in the original color, although dif- 
ferent quarries in the same state, and often in the same 
locality, may produce a wide range of colors in both 
“permanent” and “weathering” slates. 

To take the fullest advantage of the various effects 
obtainable, the source of the slate, as well as its ultimate 
color effect, should be known. 


Color Nomenclature 


For the purpose of utilizing the basic natural colors 
of roofing slate available in large quantities for general 
usage, The Division of Simplified Practice of the De- 
partment of Commerce has recommended the following 
color nomenclature: 


Basic Slate Colors 


Black Grey Purple Green 
Blue Black Blue Grey Mottled Purple Red 
and Green 


These color designations should be preceded by the word 
“unfading” or “weathering,” according to the ultimate 
color effect that may be desired. 


For special treatment roofs certain quarries supply 
other colors and combinations of colors. 


Many requests were received for inclusion in this book 
of plates reproducing slate colors. After giving full con- 
sideration to the various phases and possible misconcep- 
tion which surround color reproduction, however, it was 
decided not to include such plates. Some individual pro- 
ducers have prepared plates but much confusion has been 
caused by purchasers believing and insisting that each 
slate on their roof should be an exact match in tone and 
marking with the one shown in the plate. This, of course, 
is impracticable when dealing with the eye-resting tones 
nature has bestowed upon slate with such pleasing vari- 
ations and gradations even in the same slate and between 
slates. Samples of slates or color plates furnished by 
producers can only be taken as indicative of the color 
tones of certain slates. 


All slates would be grey, the commercially known slate 
color were it not for the coloring minerals present, for 
example, chlorite in the greens, hematite in the purples 
and hematite and iron oxide in the red. (See page. 75 
for table of Mineral Constituents of Slate.) 


Dalen cl Eee hOB eS 


AMERICAN ROOFING SLATES 


Available in Commercial Quantities in All Thicknesses Unless Otherwise Noted 


COLOR DESIGNATION 


Blue-Grey 


Blue-Grey 


Unfading Grey 


Grey 


Grey-Black 


Blue Black—Hard Vein 


Unfading Black 


WHERE QUARRIED 


BRIEF DESCRIPTION 


Lehigh-Northampton Counties Penn- 


Probably the best known, most widely used and most accessible 


sylvania. Veins extend through entire of the basic slate colors. Sales records substantiate this fact as 


slate zone. 


Near Esmont, Virginia and the Arvonia 
Belt of Buckingham and Fluvanna 
Counties, Virginia. 


Northampton County, Pennsylvania. 


Western part Vermont, Washington 
County, New York. Veins extend 
through entire slate zone. 


Western part Vermont, Washington 
County, New York. Veins extend 
through entire slate zone. 


Chapman Quarries, Pa., and adjacent 
part of Northampton County, Pa. 


Peach Bottom, York County, Pa., and 
adjacent part of Maryland. Piscatsquis 
County, Maine. 


the largest shipments of commercial standard slates are made 
from this district. Production capacity of quarries now in opera- 
tion assure architects and the public of unlimited supply of this 
popular color. Just as it is the more generally recognized slate 
color so is it also the base in cost or price tables of distributors 
and roofing contractors and nearly all of the latter carry it in 
stock. Because its blue grey tones harmonize so well with 
nature’s other handiwork “The Blue Sky”’ may explain why it 
is so frequently selected for the “roof over his head”’ of every 
man and by architects in carrying out their effects desired. 


Acres of these slates have been specified and shelter vast numbers 
of the state, federal and other public and private institutional 
buildings. : 


To more nearly portray the true color characteristics of these 
Pennsylvania slates they have been designated ‘‘Blue-Grey.” 
Some architects and older roofers may still continue to refer to 
them as Pennsylvania black, but to avoid confusion and chance 
of receiving ‘‘Black-Bed”’ slates (Note 2) architects, builders, 
roofers and others are cautioned to use this classification 
“Blue-Grey”’ as the color designation. Some splendid color 
combinations have been evolved by working together the different 
shades of these slates, or blending them with the weathering 
greens of Vermont or with the clear purples where a dark under- 
lying tone is desired. 


A tough durable Slate and one which makes an especially beauti- 
ful roof. This slate is notable for a peculiar luster giving very 
attractive lights and shadows on the roof. 


Very popular with architects because of their soft grey tones 
which harmonize so well with almost any type of wall surface. 
Unusual transverse strength. Characterized by extremely large 
quartz crystals and sericite flakes. 


Considerably lighter in tone than Blue-Grey slates of Pennsyl- 
vania. In combination with clear purples provides an excellent 
mixture where dark value underlying tone is preferable to a 
singleness of color. Some weather and some are unfading. 


Available in light and dark shades in either plain or mottled 
effect. Some are unfading and some weather. Most of the grey 
slates are mottled by streaks of darker grey and for this reason 
are often used to advantage with other slates. 


Exceptionally hard durable slate, having one or more hard veins 
running across the slate. These veins produce a texture and 
color effect very much desired. The color tone grows darker 
with exposure to elements. 


Peach Bottom Slate generally is heavier than many other slates and 
has a rougher appearance, and it is of the unfading color group. 
Markedly graphitic. First American roofing slates quarried. 


Monson roofing slate, quarried in the town of Monson, Maine 
has long been known as one of the strongest and best roofing 
slates produced in this country. It is an unfading black slate 
having a slight lustre, available only in standard thickness of 
335". Nothing over this thickness is produced except on occasional 
and special orders. 


INGA Os NGAR ee og laAG FRY avArSsS.0> Ci beAvI I OON 


Unfading Green 


Weathering Green 


Unfading Purple 


Unfading Mottled 
Purple and Green 


Variegated Purple 


Unfading Red 


Freaks 


Western part Vermont, Washington Available in light or dark shades. Whatever fading or weathering 
County, New York. Veins extend takes place is so uniform that a permanently green roof color 
through entire slate zone. is assured. 


Western part Vermont, Washington Not quarried in commercial quantities in northern part of pro- 

County, New York. Veins extend ducing zone. Available in light and dark shades. Exceedingly 

through entire slate zone. strong and tough, of excellent texture. Upon exposure to the 
elements some of these ‘‘weather”’ and are transformed into soft 
tones of brown, buff and gray while others retain their original 
shade. This weathering action of the elements serves to beautify 
a roof of this material and in no way affects the durability of the 
slate. They harmonize with almost any style of architecture and 
are used on buildings of every description. Quarries now in 
operation assure architects and the public an unlimited supply of 
this popular and most widely known and used of Vermont basic 
slate colors. Carried in stock by many roofing contractors. 


Western part Vermont, Washington Because of tremendous demand for purples in graduated roofs of 
County, New York. Veins extend assorted colors, it is now difficult to furnish clear purples in large 
through entire slate zone. quantities. 


Western part Vermont, Washington No two slates have exactly the same marking or colors. They con- 

County, New York. Veins extend sist of slightly varying shades of purples, available in light and 

through entire slate zone. dark tones, sometimes almost clear, frequently clouded with 
spots or traces of green, others with light and dark clouds of 
purple, while occasionally there are some having only a purplish 
tint that might other wise pass for Green Slate. 


Western part Vermont, Washington These slates are of a predominating purple tone, some having 

County, New York. Veins extend spots or streaks of green of varying size. In a small percentage, 

through entire slate zone. too, green may predominate with only tints of purple. As in the 
case of other weathering Vermont slates, a percentage change 
upon exposure to harmonious shades of brown, while others 
present an unchanged appearance. 


Washington County, New York only. The only place in the U.S. so far where red roofing slate has been 
found in deposits of sufficient size to insure profitable operations. 
Excellent in color, cleavage and strength. The color becomes 
more pleasing with age. A study of the price lists of slate dis- 
tributors shows this color as the most expensive. 


There are delightful combinations or variations in these colors available only for roofs of special 
treatment. Because of their color they have been termed freak slates. They are just what the name 
implies—freak slates from rock formations centuries old, of a character that will not permit splitting 
under 14” in thickness and from this up to 2” for architectural roof purposes. A great array of 
colors are available, comprising Opals, Bronzes, Buffs and Browns, and others so varied and unique that 
when displayed en masse one is reminded of a beautiful tapestry. They add charming contrasts and 
character to a roof. Some of them may not be true slate in every quality that has won for this stone its 
centuries of sheltering utility, but even should they have no salvage value, they have so enhanced the 
beauty of the building they have adorned as to fully repay the investment. 


Notes: 


(1) 


(3) 


Slates from Pennsylvania, especially in a graduated roof, are being widely used to give a wonderfully 
pleasing color effect by calling for a mixture of blue-black, blue-grey and grey. If so stipulated, the 
surface or texture may also be had rough and knarled as well as the smooth or standard finish. 


One other grade known as “Black Bed” is quarried occasionally in Pennsylvania. Due to an excess 
content of carbonaceous impurities experience has shown that after many years exposure these slates 
weather out and some slight discoloration and surface deterioration takes place. The members of this 
Association warn against the use of such slates except on temporary buildings or isolated rural dis- 
tricts. Through research and the strenuous efforts of the members of the Association only small quantities 
of such roofing slates are now available as this rock is being diverted into school slates, bulletin black- 
boards and other uses for which it is ideal. Considering its centuries of sheltering utilization, roofing 
slate presents a protection record difficult to equal and few failures of slate roofs recorded even after 
many years of service have chiefly been traced back to this ‘‘Black Bed” slate or other slates of high im- 
purity content. 


The demand for more careful selection of color tones in furnishing of architectural roofs has led to a 
more thorough analysis and inventory of the supply. Special characteristics of certain beds or veins in 
different or even the same quarries produce graduations of weathering tones which require utmost knowl- 
edge by roofer of intimate color effect desired on a roof of special treatment so that slates of this class, 
when used, may be obtained from a quarry which will meet the requirements as nearly as it is humanly 
possible to be predetermined. Inventive genius some time may eliminate the uncertainty of forecasting 
or knowing exactly the ultimate color to which slates may weather. The U. S. Bureaus of Standards 
and Mines and the research engineers of the National Slate Association are working on the problem. 


9 


SEL AS Ey eeneO SORE 7S 


American Roofing Slate Deposits Now Being 
Quarried 


Active roofing slate quarrying in the United States 
is confined to the states of Maine, Maryland, New York, 
Pennsylvania, Vermont and Virginia, the chief produc- 
tion of Pennsylvania is from the Lehigh district, in- 
cluding parts of Northampton and Lehigh Counties. The 
Peach Bottom district extends from York and Lancaster 
Counties, Pennsylvania, across the line into Harford 
County, Maryland. (See Map, page 84.) 

The active Vermont district lies in Bennington and 
Rutland Counties, and extends into Washington County, 
New York. The Maine slate deposits occur in Pisca- 
taquis County, about the center of the state. Virginia 
operations are now conducted only on the Arvonia belt 
of Buckingham and Fluvanna Counties and near Esmont. 

A number of other deposits have been worked in the 
past and may be worked again, but are now idle; others 
have not yet been developed. A few others are being 
worked now exclusively for crushed and ground slate. 

In Canada slate has been quarried chiefly in Richmond 
County, Quebec, though some slate has been produced in 
Nova Scotia and in British Columbia. Slates have been 
obtained from the shores of the Bay of Islands and 
Trinity Bay, Newfoundland. No Canadian quarries were 
in operation at time of publication of this book. 


Grading 


Practically all producers have their own trade names 
and “grades” for slate for “Textural” and “Graduated” 
roofs and the distinguishing features of each should be 
familiar to the architect or owner before specifying. 

The National Slate Association has on file a complete 
list of registered trade names of the various slates. 

With respect to the characteristics of slate, which have 
their effect upon grading, Dr. Oliver Bowles, Mineral 
Technologist of the U. S. Bureau of Mines says, in “The 
Characteristics of Slate” paper delivered before the 
American Society for Testing Materials, June, 1923: 


“Slate is of medium hardness, very fine grained of low 
porosity, great strength and consists essentially of insoluble 
and stable minerals that will withstand weathering for 
hundreds of years. Some slate in Pennsylvania contains 
ribbons which consist of narrow original beds usually con- 
taining carbon, and darker in color than the body. There 
is tendency for some ribbons to contain an excessive amount 
of the less resistant minerals and they should not appear on 
exposed surfaces.” 


Some Pennsylvania slate contains ribbons and the output 
of some quarries in this district is divided into two classi- 
fications known as “Clear” and “Ribbon.” 

The characteristics which are commonly accepted as 
affecting the appearance of the slate on the roof namely 
the surface, straightness, condition of the corners and 


10 


Figure 6. Smooth and Rough Slates 


thickness are used to determine the “Classification” or 
so-called “Grade” into which the quarries divide their 
product. 


Commercial Standard Means Properly Graded 


The classification below applies only to slate less than 
YY," in thickness for “Standard” roofs. 

When specifying “commercial standard roofing slate” 
it is unnecessary to further cover the essential character- 
istics or grading points to be considered by slate in- 
spectors in selecting and piling the slate in the storage 
yards at the quarries. The term “commercial standard” 
embodies certain grading standards which govern the 
selection of slates for shipment and are as much a part 
of the process of preparing the slate slabs for roofing 
purposes as the splitting or any other operation. 

It is to be regretted that it is impracticable to have one 
standard for all parts of the country. It will be realized, 
however, that this is impossible due to some slates con- 
taining ribbons while others are clear, some having a 
rough surface, others a smooth surface, and certain other 
distinguishing features which must be given consideration. 

In the past many architects have thought it necessary 
to specify roofing slate by the name of a town or by 
designated directions from certain towns. That this is 
too restrictive and unnecessary is apparent when it is 
realized that any particular color or kind of slate veins 
may extend through an entire region. 

A Number Two Slate comes from the same bed as the 
Number One and is only so classified because of surface 
characteristics. A knot or knurl or rougher texture on 
surface of one slate of a pile split from the same slab 
does not change its mineral constituents. It is not a 
manufactured or artificial product which can be varied 
by formula or human avarice to cut down on any ex- 
pensive ingredient. 


NGS le ON TAR 


Delt Lege oa OGIeA Tel OcN 


Architects and others may rest assured that their speci- 
fication of “Commercial Standard roofing slates in ac- 
cordance with the grading standards of National Slate 
Association” will obtain all the essential characteristics 
and quality as though they were to prescribe all the fol- 
lowing details of grading standards used at the quarries. 


Lehigh-Northampton District, 
Pennsylvania 
There are two grades of Commercial Standard Roofing 
Slates produced in Lehigh-Northampton District, Penn- 
sylvania, viz: 


Number 1—Clear Dark blue, blue-grey, or grey in color, 


uniform throughout. 
Similar in all respects to No. 1 Clear 
except for the presence of one or more 
bands or “‘ribbons”’ which are not ex- 
posed when on roof. 


Number 1—Ribbon 


The following grading rules apply to each of the 


above grades: 
Surface Reasonably smooth straight cleavage 
full length of slate both front and back. 
The maximum bend shall not exceed 
Yj” in lengths up to 16”, nor exceed 
34” in lengths from 16” to 24”. 

Shall be free from knots or knurls that 
in any way interfere with the safe 
conveyance or the laying of the slate 
on the roof. 


Reasonably full corners on exposed 
ends. No broken corners on covered 
ends that would sacrifice nailing 
strength, or the laying of a water tight 
slate roof. 


625 to 750 pounds per square depending 
on quarry and color. 


Approximately 7”. 


Texture 


Corners 


Weight 
Thickness 


In a few Pennsylvania quarries they are also producing 
two other grades: 


Medium Same as No. 1 Clear except that texture 
is somewhat rougher—less uniform in 
thickness. Weight 700 to 725 pounds 


to square. 
Same as No. | Ribbon except texture is 
somewhat rougher and ribbons may 
appear on exposed surface of slate after 
it is laid on the roof. 

Nore—Large quantities of No. 2 Ribbon roofing slates are 
used for damp courses or dampproofing of masonry construction. 


Number 2—Ribbon 


Chapman and Hard Vein Quarries, 
Pennsylvania 
There are two grades of Commercial Standard slate 
from Pennsylvania Chapman and Hard Vein quarries, 
viz., No. 1 and No. 2, both having one or more hard veins 
running across the slate. 


Number 1 
Surface Reasonably smooth straight cleavage 
full length of slate both front and back. 
The maximum bend shall not exceed 
1%" in lengths up to 16”, nor exceed 
34” in lengths from 16” to 24”. 


it 


Shall be free from knots or knurls that 
in any way interfere with the safe 
conveyance or the laying of the slate 
on the roof. 


Texture 


Corners Reasonably full corners on exposed 
ends. No broken corners on covered 
ends that would sacrifice nailing 
strength, or the laying of a water tight 
slate roof. 


a 


Thickness Approximately 35”. 


Weight 650 Ibs. to 700 lbs. per square. 
Number 2 
Surface Same quality as No. 1 but a rougher 
surface. The veins showing more 
prominent. Not quite as uniform in 
thickness as No. 1. 


Texture 


Corners Reasonably full corners on exposed 
ends with no broken corners on covered 
ends that would sacrifice nailing 
strength or the laying of a water tight 


slate roof. 


Weight 670 lbs. to 725 lbs. per square. 


Vermont and New York 
There is only one grade of Commercial Standard Roof- 
ing Slates from Vermont and New York. 


Surface Reasonably smooth straight cleavage 
full length of slate both front and back. 
The maximum bend shall not exceed 
4" in lengths up to 16”, nor exceed 


34" in lengths from 16” to 24”. 


Shall be free from knots or knurls that 
in any way interfere with the safe 
conveyance or the laying of the slate 
on the roof. 


Texture 


Corners Reasonably full corners on exposed 
ends. No broken corner on covered 
ends allowed that would sacrifice nail- 
ing strength, or the laying of a water 


tight slate roof. 


Weight 650 lbs. to 800 lbs. depending on quarry 


and color. 
Thickness 


NotrEe—‘‘Smooth”’ does not mean an absolutely even face and 
back, because the natural characteristics of the rock render 
this impossible. The word “smooth” is therefore used rela- 
tively only. The rougher slates are selected for use on other 
than the standard type of roof. 


Approximately ;”. 


Monson District, Maine 


There is only one grade of Roofing Slate from the 
Monson Maine district. 


Surface A smooth slate with grain running the 
length of slate. 

Corners Reasonably full corners on exposed ends. 

Weight Approximately 725 pounds per square. 

Thickness 35" standard thickness. 


Peach Bottom District 
There is only one grade of Commercial Standard Roof- 
ing slate from the Peach Bottom district. 


Surface Reasonably smooth, straight cleavage 


out of wind. 


SL Aa ER OOF 


Corners Reasonably full corners on exposed 
ends. Some corners are allowed off 
on ends under cover, but not enough 
to damage its service. 

Weight About 700 lbs. to 750 Ibs. per square. 

Thickness Approximately 35”. 


Virginia 
There is only one grade of Commercial Standard Roof- 
ing Slate from Esmont district and other Virginia 


quarries. 

Surface Exceptionally smooth straight cleavage 
full length of slate both front and back. 

Corners Reasonably full on exposed ends. No 
broken corners on covered ends that 
would sacrifice nailing strength or the 
laying of a water tight slate roof. 

Weight Practically uniform about 700 lbs. per 
square. 

Thickness Approximately 7”. 


Nore—The rougher slates are selected for use on other than the 
standard type of slate roof. 


Quantity 

In the United States slates are sold by the “square.” 
A “square” of roofing slate is defined by the U. S. De- 
partment of Commerce, Bureau of Standards, in Simpli- 
fied Practice Recommendation No. 14, as follows: 


“A Square of Roofing Slate—A square of roofing 
slate means a sufficient number of slate shingles of 
any size to cover 100 square feet of plain roofing 
surface, when laid with approved or customary 
standard lap of 3 inches. Slates for surfacing flat 
roofs are usually laid tile fashion, without lap, in 
which case a square of slate would cover an area 
greater than 100 square feet.” 


The quantity per square varies from 686 pieces for the 
10” x 6” size to 98 for the 24” x 14” size, which includes 
the allowance for a 3” head lap. 

It should be noted that for roofs of comparatively little 
slope where a 4” lap is required, an additional quantity 
must be provided. For steep roofs or siding, where a 
lap of 2” is sufficient fewer slates will be necessary. 
Slate, however, is always sold on the basis of quantity 
required for a lap of 3” even for flat roofs. 

The data under the next three headings is quoted from 
Simplified Practice Recommendation No. 14. 


ROOFING SLATE 


In accordance with the unanimous action on January 
23, 1924, in New York, N. Y., of the joint conference of 
representatives of manufacturers, distributors and users 
of slate for roofing purposes, the United States Depart- 
ment of Commerce, through the Bureau of Standards, 


12 


recommends that recognized sizes and nomenclature be 
reduced to those shown below. 


TABLE 1.—Dimensions of Slate Shingles for Sloping Roofs; 

Minimum to a Square 

[Each size split! to thickness of 3, 14, 3%, %, 34, 1, 14%, 1%, 
184 and 2 inches.?] 


Minimum Minimum 
Face Face 
dimensions* aes dimensions* ee 
in inches (3” lap) in inches (3” lap) 
10 by 6 686 16 by 10 22) 
10 by 7 588 16 by 12 185 
10 by 8 515 18 by 9 213 
12 by 6 533 18 by 10 192 
12 by 7 457 18 by 11 175 
I2 by 8 400 18 by 12 160 
12 by 9 355 20 by 10 169 
12 by 10 320 20 by 11 154 
l4by 7 374 20 by 12 141 
14 by 8 ByAT 20 by 14 121 
14 by 9 290 22 by 11 138 
14 by 10 261 22 by 12 126 
14 by 12 218 22 by 14 109 
l6 by 8 Ql 24 by 12 115 
l6 by 9 246 24 by 14 98 


1The art of splitting slate blocks consists in progressively reducing 
resultant halves, until the desired roofing slate thickness has been 
reached or approximated. This hand-wrought characteristic appeals to 
architects and owners. It is not a simple matter to precisely control 
the splitting of this natural rock, nor can a uniformity of thickness 
throughout be assured. The recommended range of thicknesses to be 
aimed at by operative splitters will meet all normal requirements, and 
will insure the maximum of economy in the utilization of the many 
sizes of quarried blocks. 

“It is customary to regard a thickness falling between two standard 
thicknesses as a ‘‘special,’’ and it is the practice to base the price of 
the ‘‘special’’ upon the greater of the two standard thicknesses. 

°For thicknesses one-half inch and more, it is not generally con- 
sidered practicable to use lengths that are less than 16 inches, 
although for roofs of special treatment it may be done in small quan- 
tities. (But on large projects it will be found more economical to allow 
16-, 18- and even 20 inch lengths than to specify only the 16-inch mini- 
mum.) In carrying out a desired design on special roofs, it is some- 
times necessary to make shingles longer than 24 inches, in which case 
the thicker slates are used. 


TABLE 2.—Dimensions of Slate Shingles for Flat Roofs 


[Each size split to following thicknesses: For ordinary service, 
75 inch; for promenade and extraordinary service, 4 inch and 
3¢ inch] 

Face Dimensions, In INCHES 


6 by 6 10 by 6 12 by 6 
6 by 8 10 by 7 12 by 7 
6 by 9 10 by 8 12 by 8 


SIZES OF SLATE FOR MISCELLANEOUS PURPOSES 


It is recommended that smaller slate, such as 12 or 
14 inch lengths, be used in covering pents, porch and 
dormer roofs and sides, and garage or other low-roofed 
buildings. This practice is also recommended even in 
situations where the main roof is of larger slate. 

Owing to the fact that certain sizes of slate may be 
more available than the size called for in the specification 
or order, it is recommended that architects, builders, 
engineers, and contractors provide for alternate selection 
on usual slate roofing installations. In this connection, 
particular attention is also called to the increasing use 


of random widths of the desired lengths, and to the fact 


Nee GOR N aA 


Sele Ae eee Aor ou) Cano be OFIN 


that architects are adopting this practice. While slate is 
plentiful, such practices will bring about the elimination 
of waste of an important natural resource, and will obvi- 
ate the necessity of waiting for specified sizes while an 
accumulated finished stock of other usable sizes is avail- 
able and accessible. 


DIMENSION NOMENCLATURE 


COMMERCIAL STANDARD THICKNESS (that is, average or 
basic.—The terms “3/16-inch slate,” “full 3/16-inch 
slate,” or “not less than 3/16-inch slate” indicate a desire 
for a hand-picked selection, regardless of the added labor 
and cost. “Commercial standard” is the quarry run of 
production, and shows tolerable variations above or be- 
low 3/16 inch. For the thicker slates, however, reason- 
able plus tolerances only are permissible; thus a 14-inch 
slate must be a full 14 inch or thicker. 


W eight 


A square of slate on the roof, i.e., enough slate to 
cover 100 square feet of roof surface with a standard 3” 
lap, will vary from 650 to 8,000 pounds for thicknesses 
from the commercial standard 3/16” to 2”. 

The commercial standard thickness (approximately 
3/16”) will weigh from 650 to 750 pounds per square. 
For estimating the dead load on the roof construction, 
it may be taken at a maximum of 800 pounds per square 
or 8 pounds per square foot to include slate, felt and nails. 

Slate used on flat roofs are laid without lap, the ends 
and sides being butted fairly close together. The ex- 
posure on a flat roof is thus the size of the slate used 
and the weight of slate required to cover a “square” 
of roof surface is correspondingly less. 

The weight of slate varies with the size of the slate, 
color and quarry and even sometimes in the same quarry. 
This variation may be from 10% above to 15% below 
the weights given in the following table of average 
weights of slate of different thicknesses for both sloping 
and flat roofs. 


Slate Average Weight of Slate per Square 


(100 sq. ft.) 
Thickness in 
Inches Sloping Roof Flat Roof 
Allowing for 3” Lap Without Lap 
Standard iis 700 240 
Selected full 35 750 250 
yy 1,000 335 
3% 1,500 500 
Vy 2,000 675 
34 3,000 1,000 
1 4,000 1,330 
14 5,000 1,670 
1% 6,000 2,000 
134 7,000 
2 8,000 , 


13 


ie .oieen eter 


IIBCHINE: PUSYCHED 


— 


HAND PUNCHED 


Figure 7 


Nail Holes 


No slate should have less than two nail holes. 


The 
standard practice is to machine punch two holes in all 
architectural roofing slate 14” and thicker at the quarry 
and also in commercial standard slate when so ordered. 


Four holes should be used for slates 34” or more in thick- 
ness when more than 20” in length. Holes are punched 
from one-quarter to one-third the length of the slate from 
the upper end, and 114” to 2” from the edge. Where 
four holes are used, it is customary to locate the two 
additional holes about 2” above the regular holes. 

Some architects in the past specified that all nail holes 
should be drilled and countersunk. On normal thickness 
slates, no method of drilling has been developed which 
will produce the same clean hole as by machine punch- 
ing, because the small thickness of stone at the cutting 
point is insufficient to absorb or dissipate the drilling 
force. Hence the industry, through the Association, in 
1923 adopted the machine punching of nail holes as 
standard practice. 

That the results are excellent is demonstrated by the 
fact that, when given two slates with holes punched by 
either method, architects have usually selected the ma- 
chine punched as the better and have even called them 
drilled and countersunk. 

Machine punching is preferable to hand punching. 
The term hand punching usually refers to the use 
of the double head slaters hammer having one head in 
the form of a long prong. Machine punching may be 
done either at the quarry or on the job. Hand punching 
of holes in fitting hips, etc., is, of course, necessary. 


LG 


470 4th 
> oO 
° 


= LENGTH MORE THAN 20° 4 


° 
° 


20 OR LESS: acy 


Figure 8. Location of Neil Holes 


N the laying of any roofing material workmanship is 
Ve. essential as the proper selection of the material. 
The more enduring the material the more important this 
factor becomes. Slate, the most lasting roofing material 
known, should be laid by roofers of experience and 
training. It is a mistake to assume that those without 
such experience are qualified to properly lay slate. For 


Figure 9. 
Properly Nailed 


Figure 10. 
Nail Driven Too Far 


Figure 11. 


Nail Not Driven Far 
Enough 


instance the nailing of wooden shingles and slates are 
entirely different. The heads of slating nails should 
just touch the slate and should not be driven “home” or 
draw the slate, but left with the heads just clearing the 
The opposite 
is true of wooden shingles and a man used to laying this 


slate so that the slate hangs on the nail. 


material will invariably handle slate in the same way. 
As a consequence the slate, held too rigidly in place, is 


14 


shattered around the nail hole or the head of the nail 
crushed and eventually the slate may “ride” up over the 
nail and be blown off in a heavy wind. The blame is 


Via, SLATE 


Figure 12. Starting Slate 


placed on the material whereas the real reason can be 
traced to the method of nailing. All nails should pene- 
trate the sheathing and not the joints between boards. 
This is especially important near the ridge of the roof. 
It would seem almost unnecessary to mention the fact 
that there should be no through joints from the roof sur- 
face to the felt. The joints in each course should be well 
broken with those below. Where this simple precaution 
is neglected it is possible that water may find its way 
through the joints, eventually cause the felt to disin- 


NOT LESS THAN 3° AND AS 
{| ENC NTIL: G. TLEVASTPOSSIELE 


Figure 13. Proper Jointing 


Where random widths are 
used the overlapping slate should be jointed as near the 
center of the under slate as possible and not less than 


tegrate and leaks develop. 


NGA el Or INGA, Eb 


ee Ne ele ee Once tele OUN 


3” from any under joint. Where all slates are of one 
width, this is automatically taken care of by starting 
every other course with a half slate or, where available 
and practicable, a slate one and one-half times the width 
of the others. 

With but few exceptions, the standard 3” lap should 
be insisted upon. The “standard 3” lap” or “3” headlap” 
means the lap of the slate over the second course below, 
see Figure 15. The small saving in slate through reduc- 
ing the lap will not compensate for the risk entailed of 
leakage due to the lessened amount of material over 
which water might be blown. 

A practice prevalent among many roofers is that of 
driving the slater’s stake into the roof boards. To avoid 
damaging the roofing felt, a plank should be used for 
this purpose or the stake driven into the scaffold only. 
Slaters occasionally use a metal strap as a support for 
the scaffold brackets. This practice should be discour- 
aged when these are cut off and a part left on the roof. 
They will rust in time and stain the slate in a most un- 
sightly manner. 


Figure 14. A Satisfactory Scaffold Bracket 


The foregoing applies to slating in general. The 
forming of slate hips, ridges, valleys, eaves and gables 
require a description peculiar to themselves. 


Exposure 

The “exposure” of a slate is the portion not covered by 
the next course of slate above and is thus the length of 
the unit exposed to the weather. The standard lap of the 
alternate courses used on sloping roofs is 3” and is the 
basis upon which all roofing slate is sold and the quan- 
tity computed. The proper exposure to use is then ob- 
tained by deducting 3” from the length of the slate used 
and dividing by two. For instance, the exposure for a 
24” slate is 24” minus 3” = 21” ~ 2 = 1014” exposure. 

The following table will be found of use in readily 
obtaining the proper exposure. 


15 


Exposure in Inches for Sloping Roofs 


a " an" 
Length of Slate Slope : A ) 
in Inches PSY jee ‘ 

ap 
Ag RET EO PRAT eet te SARE on plete ve 10% 
PUPAR, i BOE EEE gb nA es aL PCRS bes ae Ie RE Page 9% 
IAD sn ies brerdp hs BAe DA eC OL eee 8% 
LORE ars ers Alcs freon A eee ee en 7% 
i Gree ee pe ete rd waa eis Lote 6% 
Aa Ne wr Seen Ses Ain eke c(t eee 5% 
des dn once Sic AGS CaENOT Gee Ges PARE Rn Tea LS Een 4s 
VU ssc tch SOE nc Se ote RRS ae neta ak a meine 3% 


Sloping roofs having a rise of 8” to 20” per foot of 
horizontal run should be laid with the 3” lap. Buildings 
located in the southernmost parts of the country or on 
the Pacific slope may however be safely roofed with a 
lap of 2” providing a high standard of workmanship is 
otherwise maintained. For steeper roofs, such as the 
Mansard and others nearly vertical in plane a 2” lap will 
usually be found sufficient. In some sections of the 
country it is customary to increase the lap to 4” when 


the slope is from 4” to 8” 


per foot, while in other parts 
Flat roof 


construction should be used for slopes less than 4” per 


the 3” lap is considered entirely adequate. 


foot. For vertical walls or siding use 2” lap. 


Ridges 

There are two common methods of finishing the ridge 
of the roof. These are usually known as the “Saddle 
Ridge” and “Comb Ridge” but each may have other 
names and certain variations in laying according to 
local practice. In Figure 16 are illustrated two types 
of saddle ridge which are known respectively as the 
“Saddle Ridge” and the “Strip Saddle Ridge.” In the 
first of these, the “Saddle Ridge,” the regular roofing 
slates are extended to the ridge so that pieces of slate on 
the opposite sides of the roof butt flush. On top of the 
last regular course of roofing slate at the ridge is laid 
another course of slate called the “Combing Slate” and 
the pieces on the opposite sides of roof butted flush. The 
combing slate is usually laid with the grain horizontal 
and should be of such width that the exposure or gauge 


Figure 15. Lap and Exposure 


POINT WITH ELASTIC CENENT 


evs GNX Th Veg), 2 LATH COMBING SLATE 
SOMETIMES OMITTED 


GY 


PLASTER LATH 
SOMETIMES OMITTED 


COMBING SLATE 
ELASTIC CEMENT 


SECTION ROOFING SLATE 


OIRI TZ MOAV OEE BRY OGE 


BUTT JOINTS 


COMGBING. SLATE LAID WI/TIlt GRAIN 
VERTICAL 

COMBING SLATE 

ELASTIC CEMENT- 

ROOFING SLATE 


DETAIL 
COMBING SLATE LA/D WITH GRAIN HORIZONTAL 
WHEN THE COMBING SLATE ARE LAID ALTERNATELY IMALLER SLATE (OF VW PROPER, 15/1 Z2E (MAY Sie 
PROJECTING ON EITHFR SIDE OF THE RIDGE, USED WO GIVE SAME VEXPOSUCRENMASE GE OWE (3) 
THIS TYPE 1S KNOWN AS A "COXCOMB’ RIDGE. OF ROOF COURSES. 


FIGURE 16. STANDARD DETAILS SLATE RIDGES—NATIONAL SLATE ASSOCIATION 


Ne Agee OaNe as |: 


Sele ee ee ee Oot On GelAm lL TeOgN 


of the roof is maintained approximately uniform. For 
example if 20” x 12” slates are used on the roof with an 
814” exposure, 12” x 8” slates laid horizontal could be 
used on the ridge. It will be noted in Figure 16 that the 
combing slates overlap and break joints with the under- 
neath slate. In this way all the nails in the combing 
slate are covered by the succeeding slates except the 
nails in the last or finishing slate on the ridge and these 
nails should be covered with elastic cement. In Figure 
16 it will be seen that only two nails are used in each 
slate. For this reason the end of the slate which is not 
nailed should be held in place by elastic cement. The 
joints on top of the ridge formed by the butted edges of 
the combing slates should be filled in with elastic cement 
when subject to heavy rainfall. Some roofers do not use 


BLASS Wood 


BEND DOKN TO SLATE 


THE COPPER MOLD 45 SECURED 
IN PLACE BY BRASS WOOD 
SCREWS ~- CLAMPS AS SHOWN 
MAY BE UVSED MADE OF $e +/* 
BRASS AND PLACED ABOUT 30" 
APART L£/ITHER INSIDE OR 
OUTSIDE OF THE MOLD 

JF PLACED INSIDE - THE CLAMPS 
ARE RIVETED TO THE MOLO 
BLE FORE ERECTION 


Z HOS 
THREE TYPES OF *1/P OR RIDCE 
FLASHING SOR A SLATE ROOF 


Figure 17 


any elastic cement on either the hips or ridges, but this 
practice is not recommended except under favorable cli- 
matic conditions. The nails should be arranged to go 
In 


some parts of the country it is customary to clip the 


between the joints of the slate immediately below. 


upper edges of the last roof slate as shown in the draw- 
ing, Figure 16, Plate 1. Many architects prefer to keep 
the grain of the slate vertical, using the same type of 
ridge with top or combing slate of the same width as the 
regular roofing slate and the length the same as their 
exposure. In such cases the starting slate could be a 
“slate and a half” in width rather than a “half slate.” 
Another type of saddle ridge is that known as the 
“Strip Saddle Ridge.” This ridge is laid in a similar 
manner to the above except that the combing slates do 
not overlap but butt flush and each combing slate has 


LZ, 


Figure 18. Ridge and Closed Valley 


four nails. The combing slate may be the same width 
as the regular roofing slate or narrower as the designer 
The nails should be covered with elastic 


cement and the edges of the combing slates set in elastic 


may wish. 


cement as shown in Figure 16. 

The “Combing Ridge” is laid in the same manner as the 
“Saddle Ridge” except that the combing slate of the north 
or east side extends beyond the ridge line as shown in 
the detail, Figure 16. This extension should not be more 
than 1”. This type of ridge may be laid with the comb- 
ing slate having a grain vertical or horizontal. In either 
case, the edge of the slate should be set in elastic cement, 
as shown, and the nails covered with elastic cement. If 
the top or combing course is projected 1/16” to 14” 
above the under top courses, it will make a much better 
finish and will be more easily filled with elastic cement. 

A variation of this type of ridge is known as the “Cox- 


Figure 19. Fantail Hip 


Se Am Shien eOaQOehas 


comb Ridge” in which the combing slate alternately pro- 
ject on either side of the ridge. 

It will be noted that in Figure 16 the top courses 
of the regular roofing slate have the edges set in elastic 
cement. This is done to avoid their lifting under action 
of the wind and should in no sense be construed as being 
necessary from the standpoint of weather-proofness. 


Hips 

There are several methods of forming hips on slate 
roofs, some of which are illustrated in Figure 22. These 
are the ones most common in all sections of the country 
although they may be known by other names than those 
given herein. 


Figure 20. Open Valley 


The “Saddle Hip” may be formed by placing on the 
sheathing forming the hip one or two plaster lath or a 
31%” cant strip and running the roofing slate up to this 
strip. On top of the cant strip and the slate are laid the 
hip slates which are usually the same width as the ex- 
posure of the slates on the roof, although they may vary 
in width on different classes of work. 

It will be noted in the detail Figure 22, Plate 1, 
that the four nails used to fasten the hip slate to the roof 
are driven into the cant strip and do not go between the 
joints of the slate. The heads of these nails are then 
covered with elastic cement and the lower part of the 


18 


next slate bedded therein as shown. Elastic cement is 
also placed on the joint between the roofing slate and 
the plaster lath and on the peak of the hip before the 
hip slates are laid. A variation of the “Saddle Hip” is 
known as the “Strip Saddle Hip” which is used on less 
expensive work and may be formed of narrower slates 
laid with butt joints which do not necessarily line up 
with the course of the slate on the roof. 

Another type of hip is that known as the “Mitred Hip.” 
In forming this type of hip the slates forming the roof 
courses and the hip are all in one plane as is shown in 
Figure 22, Plate 2. The hip slates should be cut accu- 
rately to form tight joints and the joint should be filled 
in with elastic cement. The nail holes should be so 
placed as to come under the succeeding hip slate. 

A variation of this type of hip is that known as the 
“Fantail,” shown on Figure 22, which is laid in the same 
manner as the “Mitred Hip” but which has the bottom 
edge of the hip slate cut at an angle to form a fantail. 

Another very popular type of hip is that known as 
the Boston Hip. In this type of hip the slates are woven 
in with the regular courses of the roofing slates, as shown 
in the detail. The nails are then covered with elastic 
cement and the lower part of the succeeding slate bedded 
therein. 

It is sometimes recommended that metal or slip flash- 
ings be woven in with each course of “Mitred Hips” but 
this is usually unnecessary if proper care and workman- 
ship are exercised in cutting, fitting and bedding the hip 
slates.. There are some roofers who do not use elastic 
cement on the hip slates and secure satisfactory results. 


Valleys 


Of the two methods of forming the valleys the first, and 
without doubt the more satisfactory, is the open valley. 
The second, known as the closed valley, is considered by 
many to be the more pleasing in appearance and is much 
used on high-grade work. Variations of the closed val- 
ley, frequently used in connection with the Graduated or 
Textural roofs, are the “round” valley and the “canoe” 
valley. 

OPEN VALLEY 

The open valley is formed by laying strips of sheet 
metal in the valley angle and lapping the slate over it 
on either side, leaving a space between the slate edges to 
act as a channel for water running down the valley angle. 
The width of the valley, or the amount of space between 
the slate edges should increase uniformly toward the 
bottom. The amount of this increase, or taper, has been 
determined as | inch in 8 feet. For example, in a valley 
16 feet long, the distance between slates will be 2 inches 
greater at the bottom than at the top, as the width in- 


BEVELED STRIP OR ONE OR TWO 
PLASTER LATH SOMETIMES 
OMITTED. HIP SLATES ARE 
SOMETIMES SMALLER SLATES. 
ON LESS EXPENS/VE WORK 
S7R/P SADDLE HIPS ARE 
LAID WITH BUTT JOINTS oy 
WHICH DO NOT ALWAYS om ( i 
{| ‘| 


| 6 ee eee : 
= SECTION A-A’ AND NY 
PERSPECTIVE VIEW 


CUE SIDE qn? OF SADDLE HIP 


SECTION AA’ AND 
PERSPECTIVE VIEW 
OF MITRED HIP 


JERE UOMO Tad (TEM ANA E7/ P 


FIGURE 22. STANDARD DETAILS SLATE HIPS--NATIONAL SLATE ASSOCIATION 


| 2ESTEEELTTTITT  RACRRCRATRL'S) WLLL TTA ETT TT 
PE OS IOS 5 egos FF SSS SSS SET OS 
TOITATs CLIN LITTT EO CLALIT D SOLE E TERT TL ID O8 Oe LITO Y LE 
L —t 


SLATE 


VOT gn eA LI IA LALLA LAAT LLY 
BS SSTSS SI SSS TSS SSIS SSS SSS SSS I 
L777 Xi LITT a Oe NE 


0b OOF OPTED | hhh hack hn 
P77 pn) >< | 
aa See 7 eG 
ena ¥ 
. 
. . 2 sf 


TABLE CON LUTE UMW AVENUES — (ROLY MY 
W/TH EACH COURSE OF SLATE 


ii FLASIANG [SHEET 
1} APPED\ \3" 


FOO. 1D Ve (5) 


Vi AiLgalaey 


‘UNDER EAVE” 
OR STARTER 
SLATE 


RS SSS 
RM 


SECTION 8-8 


FLASHING 
ROOF SHEATHING 


SWSGIMKOM (GAE, (4) (6) 


FIGURE 23. STANDARD DETAILS SLATE VALLEYS, EAVES AND GABLES—NATIONAL 
SLATE ASSOCIATION 


(We IRE CHOY 


ING Ae el ORNAS I 


Selly ete eS OnGuls ARTs IO ON 


Closed Valley 


Figure 21. 


creases at the rate of 14” in 8 feet on each side of the 
valley. This permits a uniform width of about 2/3 the 
width of the slate under the slate adjacent to the valley. 
The difference in width or taper allows the slate to be 
laid closer to the valley at the upper than the lower end 
and takes care of the increase in water received. This 
tapering of the valley also has the very practical effect 
of allowing any ice which may form to free itself and 
slide down as it melts. 

This increase of width in the valley must be allowed 
for in placing the flashing strips. Valley flashings are 
generally laid in pieces up to 8 feet long. The best 
theoretical manner of taking care of the taper would be, 
of course, by tapering the sheets. As this involves con- 
siderable additional expense in labor and material it is 
often more practicable to use sheets shorter than 8 feet 
and increase the width of each sheet an amount sufficient 
to take care of the taper. This increase in width amounts 
to 1/8 of an inch per foot. The increase in the widths 
of succeeding sheets of various lengths necessary to take 
care of this taper is shown in table No. 3. Figure 23 
shows the method of installing the sheets. 

The slate should start 2” each side of the valley center 
at the top and should taper away from the center at the 
rate of 14” for every eight lineal feet. The metal flashing 
should be of sufficient width to extend up under the slate 
not less than 4” (preferably 6” to 8”), and as far as is 
possible without being punctured by the slating nails. 

Where the two roofs forming the valley have consid- 
erable difference in slope or the roofs are much different 
in size and cause a large variation in the volumes of 
water to be delivered into the valley, the metal should 


21 


be crimped or made with a standing seam to break the 
force of the water from the steeper or longer slope and 
prevent its being driven up under the slate of the oppo- 
site side. 


TABLE 3 


Showing increase of widths of untapered sheets in a 
tapered valley. 


Length of Increase in Length of Increase in 
Sheets Width Sheets Width 
24 A 60 x 
30 15 66 i 
36 3% G2, 34 
42 ae 84 , 

48 Vy 96 if 
54 S 


Exampte: A valley is 19 feet long. The sheet extends 5 inches 
under the slates and is fastened by cleats. What width of sheets 
can best be used? As a 4-inch minimum under the slate is 
necessary two eight- and one three-foot length can be used. 
Starting at the top the first sheet would be 2+2+5+5+%+ 
44=15 inches wide. If the three foot is used at the top, the 
first eight foot sheet would be 153g or 15% inches wide and 
the second one 163% or 161% wide. 


Condensation forming on the underside of valley flash- 
ings, when not free to run off or evaporate, may attack 
It is therefore recommended that the felt be 
omitted under metals if other than copper is used. If 
felt is used under other metals they should be well 
painted on the underside. 


the metal. 


For inexpensive roofs as provided for in the specifica- 
tion for a Standard Roof the copper for valleys is laid 
flat without crimps or cleats. For high-grade work the 
copper sheets should be secured to the roof boards and 
over the felt with metal cleats from 8” to 12” apart. 


COPPER PLASHING LAID 

IN LONG SHEETS: CONT/NY- 
OVS OVER ROOF SHEATH- 
ING -THE UPPER SHEL 7 
70 LAP FOUR /MCNES Wee 
VANE LOWE SHEE]: 


Y 


f 


| N 
7 \ 
y, 


COPPER FLASHING 
ROOF GLLATH/NG 


‘SECTION O-D: 


\ 
nid 


aN 
AS ES 
FLASHING FORA CLOSLD VALLLY USINGLONG 
SHEETS UNDERNEATH SLATE 


Figure 24. Another Type of Closed Valley 


Sel Ay Eos ReOmOnies 


The edge of the sheet is turned over 14” and the bent 
end of the cleat hooked under. The cleat is then nailed 
to the roof boards with two nails and the cleat bent over 
to cover the nails. A method sometimes used on wide 
valleys with the best work is to fold the metal 4” or 5” 
from the valley line and 3” from the cleat fold. This is 
known as “Fold-over” flashing. 


CLOSED VALLEY 


The closed valley is formed with the slate worked tight 
to the valley line and pieces of metal placed under the 
slate as shown in Figure 23. The size of the sheet to be 
used is determined by the length of the slate and the 
slope of the adjoining roofs. Each sheet should extend 
2” above the top of the slate on which it rests so that it 
may be nailed along the upper edge of the roof sheath- 
ing without the nails penetrating the slate. Each sheet 
should be long enough to lap the sheet below at least 3”, 
and should always be set back of the butt of the slate 
above so that it will not be visible. These sheets are 
separated by a course of slate (Section BB). Each sheet 
must be wide enough so that the vertical distance from 
the centre of the valley to a line connecting the upper 
edges of the sheet will be at least 4”. This dimension 
depends upon the nailing of the slate which should not 
penetrate the sheets. 

Some roofers form the sheets with a center crimp 
(Figure 24), thus stiffening them and forming a straight 
line to which to set the slates, and preventing water from 
one slope forcing its way above the sheet on the other 
slope. 

Another method of forming a closed valley is shown in 


Figure 25. Round Valley 


22 


Figure 26. Eaves and Gables 


Figure 24, The sheets are laid in long pieces directly on 
the paper or felt covering the roof sheathing before the 
slate is laid. They may be of any desired length and 
should lap in the direction of the flow at least 4”. They 
should be nailed about every 18” along the outer edge, 
and care shculd be taken to avoid penetrating the sheet 
when nailing the slate. 


ROUND VALLEY 


The round valley forms a pleasing transition between 
two intersecting slopes when used in connection with the 
Graduated or Textural roof. However, if not properly 
laid out it will produce disaster and mar an otherwise 
beautiful roof. For this reason its laying should be 
entrusted only to those fitted by knowledge and experi- 
ence to do this particular work. It requires the most 
careful workmanship and experienced knowledge of the 
problem to secure a job that will be both pleasing in 
appearance and water-tight. 

Primarily the round valley requires a suitable founda- 
tion to establish the general contour. The method of 
building this foundation is described under sheathing and 
roof boards on page 40. 

The valley slates must be at least 4” longer than the 
slates used in the corresponding courses of the roof. 
The sides of the slates must be trimmed to the proper 
radius and the tops shouldered to make the slates lay 
flat. 

The round valley slates are sometimes bedded in elas- 
tic cement. If proper care is used in the trimming and 
fitting, no flashings should be necessary. Where the 
workmanship is not dependable, flashings of metal or 
prepared roofing cut to the proper radius should be used 


NG OR NP AS oper AG lt AT Sts O Gor ATT 1 OUN 


as a precautionary measure. F lashings should always be 
used wherever ice may form. 

The radius of the round valley starts as a maximum at 
the eaves and gradually diminishes to practically zero 
at the ridge. For appearance, as well as to facilitate lay- 
ing the valley slates, the distance across the eaves should 
not be less than 26”. If the roof condition will not per- 
mit this, the “canoe” valley should be used. 

The canoe valley is a variation of the round valley and 
is laid in the same manner except that the radius at 
the eaves and ridge is practically zero. The radius is 
gradually increased until it becomes a maximum half- 
way between the eaves and the ridge. 


Eaves and Gables 


The under-eave slates should start on a cant strip of 
suitable thickness, depending upon the thickness of the 
slate, to enable the second course of slate to be correctly 
laid. In the case of a cornice, this slate should project 
about 2” beyond the cant strip, sheathing or finishing 
member. The length of the under-eave slates is found 
by adding 3” to the exposure being used on the regular 
slates. Thus, if 16” slates are used, the exposure is 614” 
and the size of the under-eave slate required is 914”. Half 
slate are sometimes used, or roofing slates of the proper 
width may be laid horizontally. If the first course is 34” 
in thickness, use 34” slates for the under-eave course or 
1,” slates if the starters are 44”, although the under-eave 
and first course are sometimes made the same thickness. 

The first course of slate is laid over the under-eave 
course with the butts of both courses flush, and the joints 
broken. 


Figure 27. Laying Slate 


23 


When changing from a roof of flat slope to one of 
steeper slope as in the case of a Gambrel roof, the slate 
of the upper and flatter roof should project 2” to 214” 
beyond the steeper roof below. A cant strip should also 
be used upon which to start the slate of the roof of lesser 
slope the same as at the eaves. 

At the gables the slate should overhang the finishing 
Where 
close-clipped gables are used or the construction is such 
that the gable slates have ample nailing, this dimension 
may be increased, but the projection ought not to be too 
Also there are many inter- 


member of the verge board not more than 14”. 


great for good appearance. 
esting ways to lay “Gable end” or “Barge” slates under 
regular courses along gable ends where shadow effect is 
desired. Ways and means of using and securing all 


gable end slates depends on type of construction. 


Roofing Felt 


It should be emphasized that a standard slate roof 
can be laid water-tight on open lath without felt, as is 
often done in the South or on buildings where heat is not 
required. The thickness of the felt has little relation to 
the water-tight qualities of a slate roof. The opinion has 
been held by many that the thicker the felt, the tighter 
will be the roof. When it is realized that every nail used 
in fastening the slate is driven through the felt it will 
be seen how erroneous is this idea. Roofing felt, how- 
ever, does have three other distinct uses in connection 
with slate roofs. The felt placed as soon as the roof is 
sheathed will protect the building, when necessary, until 
the slates are laid. 

It has considerable insulating value in resisting the heat 
of the summer sun and the transference of heat from the 
inside during the winter months. Increasing heating costs 
in the colder localities makes this a factor worth careful 
The use of laths over the felt and under 
the slates to obtain an air space, a method recommended 


consideration. 


by English roofers, adds much to the insulating value of 
the felt. 

The third value of the felt is to form a cushion for the 
slate. While not of great moment in the case of commer- 
cial standard slates, its value in this respect increases as 
For the 
commercial standard slate felt weighing 14 pounds per 
square will be found satisfactory. The same weight is 
Any of the 
heavier weight felts, as 20, 30 or 40 pounds per square, 
may be used where the appropriation allows. For 
Graduated roofs, the 30 pound weight is commonly used 
when the slates are 34” or less in thickness and the 50 


the thickness and weight of the slate increases. 


ordinarily used under Textural roofs. 


pound for slates 1” or more. It is customary in some 


localities to place two layers of felt under the slate on a 


Sule ieee ReOsORhES 


Graduated roof. The first layer is usually 30 pound felt 
and the second 14 pound. This provides an extra cushion 
for the heavy slates. The joints and laps should always 
be staggered. 

The felt should be laid in horizontal layers with the 
joints lapped toward the eaves and at the ends. A lap 
of at least 3” should be used and the edges should be 
well secured to the surface over which it is laid. A lap 
of not less than 2” should be used over the metal lining 
of valleys and gutters. If metal other than copper is 
used as a lining the felt should be omitted in the valleys. 
Extend the felt over all hips and ridges at least 12” to 
form a double thickness. 

Asphalt saturated rag felt should always be used. The 
so-called “Slaters’” felt includes many types of materials 
which cannot be recommended. 


Elastic Cement 


In the past the extensive use of Elastic Cement has 
often been recommended because it was supposed to be 
necessary in order to make a slate roof water-tight. It 
is now realized that this is erroneous and that it is not 
only possible but practical to omit Elastic Cement en- 
tirely and in some localities experienced roofers have 
abandoned its use and secured absolutely water-tight 
roofs. It has even been found that in certain locations on 
the roof the use of cement may prove to be detrimental 
rather than helpful. An instance of this is under slates 
adjacent to open valleys where the cement may dam the 
water and force it back under the slates instead of per- 
mitting it to run out into the valley. 

Elastic Cement does have its value, however, and is 
used under slates forming hips and ridges to help hold 
securely in place those slates which are usually smaller 
than the regular roofing sizes and which cannot be so 
well nailed. Elastic Cement is also used for pointing the 
peaks of hips and ridges. 

The requirements which should govern the selection 
of Elastic Cement are few but important. It should be 
water-proof. It should have a high melting point to pre- 
vent the slates from slipping under the heat of the 
sun and a low freezing point to prevent its becoming 
brittle and cracking in cold weather. It is important that 
the cement should not dry out and pulverize when ex- 
posed to the air. The best grades of cement are of an 
oily, sticky nature and, considering the small amount 
ordinarily required for a slate roof, it is economical to 
use only the best quality. 

The Elastic Cement should match as nearly as possible 
the color of the slate, but it should be noted that cements 
of certain colors may fade upon exposure, and experi- 
ence only will show those that are fast and satisfactory. 


24 


Slater’s Tools 


The tools commonly used by the slater are the punch, 
hammer, ripper and stake. If much punching is done 
at the yard or on the job by the roofer, a punching ma- 
chine should be used for punching the nail holes and 
cutting the slates. It is adjustable to any size or shape, 
cuts and punches at one operation with a countersunk 
hole. The hand or mawl punch is forged from fine tool 
steel hardened and ground about 414” long with one end 
tapered. The butt end is struck with a mawl to punch 
the nail hole. 


<— AypiN.— > 


Figure 28. Slater’s Tools 


Slater’s tools are all drop forged. An approved ham- 
mer is forged solid, all in one piece, from crucible cast 
steel, with an unbreakable leather handle to avoid slip- 
ping and blistering the hands. One end terminates in a 
sharp point for punching slate, the other in the hammer 
head. There is a claw in the center for drawing nails, 
and on each side of the shank there is a shear edge for 
cutting slate. The head, point and cutting edges are 
properly tempered to withstand heavy work. The slater’s 
stock size hammer has a 12” handle. 

The ripper is about 24” long and is forged from cru- 
cible cast steel. It is used for removing broken slate and 
making repairs. A hook on the end provides a means of 
cutting and removing the slating nails. The blade is 
drawn very thin and the hook end correctly tempered for 
hard wear. 

The stake is about 18” long and T-shaped. The long 
edge is used as a rest upon which to cut and punch slate 
or as a straight edge to mark the slate when cutting and 
fitting around chimneys, hips, valleys, etc. The short 


NEG eR OUND Agen oe Am ls ee AY Seo O, IRA TION 


arm is tapered and pointed for driving into a plank or 
scaffold. 

These tools, as well as 24” stakes, shorter rippers, left- 
hand hammers or special hammers or tools, can be ob- 
tained from any slate producer distributing roofing slate 
or from manufacturers of such tools. The slater’s equip- 
ment is completed with a nail pouch, tinner’s snips, rule 


and chalk line. 
Nails 


Slate, being a permanent material, is worthy of care 
and thought in the proper selection of the various mate- 
rials used in connection with it, and especially as to the 
method of securing the slate to the roof construction. 

Like any other construction unit, a slate roof can only 
be as strong and enduring as its weakest part, and the 
majority of slate roof failures over a period of years 
may be attributed to the punching of the nail holes, the 
As has 
previously been stated, the art of properly laying and 
nailing slate is not to be discounted and belongs to men 
trained especially in the work. The punching and nail- 


nailing of the slates, or the nails themselves. 


ing of the slate have been described under the heading, 


“Laying Slate,” on page 13. 

Before nails came into extensive use, the slate were 
held in place by means of wooden pegs driven through 
the slate and hooked over the roof lath. It is the practice 
in some localities today to hang the slate to the laths or 
battens by means of heavy wire hooked through the slate 
and over the laths. This method is in general use where 
the slate is laid directly on steel construction. Copper 
nails of sufficient length to be securely hooked and 
clinched over the structural angles may also be used. 
These should have large heads and the shafts be of No. 
10 or 11 gauge metal. 

Nailing is more extensively used today than other 
methods for securing the slate, and careful attention 
should be given the characteristics of nails selected for 
this purpose. The important considerations involved are 
shape, size and material. 


For all practical purposes, the ordinary diamond point 
and smooth shaft are sufficient for a slating nail and the 
needle point is seldom, if ever, necessary or of advantage. 
The shaft, since it supports a greater weight and must 
resist a small shearing stress, should be larger than that 
of the shingle nail. To prevent the slate from being 
lifted up over the nail after being laid, the diameter of 
the head should be greater than that of shingle nails. 

The temptation to use shingle nails instead of slating 
nails should be discouraged, for the slight saving in cost 
on the entire roof cannot approach the cost of repairs 
which may develop as a result of this practice. Archi- 


29 


tects and owners should insist that the roofer use nails of 
proper size and kind of non-ferrous metals. 

The much-mooted question of the material of which 
the nails should be made must remain a matter of opinion 
and judgment until an impartial investigation shall throw 
further light upon the subject. 

It is hoped that research in this field may be under- 
taken in the near future and definite results furnished 
those interested. It is a generally accepted fact that 
copper is one of the most enduring of metals and that 
iron and steel, adequately protected from corrosion by a 
heavy coating of zinc applied by the hot-dipped process, 
Plain or ordinary galvan- 


Nails 


having a copper content, such as “yellow metal,” or 


will give reasonable service. 
ized nails should not be used for laying slate. 


“Muntz Metal” and cut zinc nails are sometimes used. 
Nails should be carefully selected and be the best grade 
of a reputable manufacturer. Recently “Cimet,” “Ever- 
dur” and similar chrome-iron alloy nails and other types 
particularly suited to resist atmospheric corrosion, have 
been put on the market. Their cost is higher than copper, 
yet for certain buildings with excessive or unusual acid 
fumes under and surrounding the slate roofs, it may 
prove economical to use such nails. Time and wider use 
of these newer types will prove whether they are or are 
not superior to copper. When cost is an item, the “Cop- 
perweld” nail, being less expensive than solid copper, 
is often used and may prove to be the satisfactory method 
of protecting the steel shaft. 

Under ordinary conditions, it will be found satisfactory 
to use 3d nails for commercial standard slates up to 18 
inches in length. Use 4d nails for the longer slates and 
6d on the hips and ridges. Thicker slates require longer 
and heavier gauge nails. The proper size may be deter- 
mined by adding 1 inch to twice the thickness of the 
slate. Where the through penetration of the sheathing 

LENGTH - INCHES 


of 1% 12 1% 


Figure 33. Full Size Nails 


DEL RAR Ere ReOLO shes 


will not ordinarily be seen, it provides evidence that 
nails of sufficient length were used. Thus a 14” slate will 
require a 4d nail which is 114” in length. Where the 
under side of the roof boards is exposed to view, as is 
sometimes the case of overhanging eaves, a nail of such 
length as will secure sufficient penetration but not be 
driven through the sheathing must be selected. 


Figure 29 Figure 30 Figure 31 Figure 32 
Copper Wire Large Flat- Regular Cut Large Flat- 
Nail. (Simi- Head Copper Copper Nails Head Cut 
lar to Steel Wire Nail. Copper 
Wire Nails)  (Slating Nail) Roofing 

Nail 


[Note difference in head of ordinary wire nail (Figure 29) 
and large flat-head wire nail (Figure 30)]. 


Nails suitable for roofing purposes are made in four 
forms, each of which has its advantages. 

The common wire nail (Figure 29) is used generally 
for nailing flashings, sheathing, and sometimes for shing- 
ling. It is not suitable for slate work, for it is of light 
gauge and small head. 

The slating nail (Figure 30), as may be seen, is espe- 
cially adapted for slating, as it is of heavy gauge and has 
a wide, flat head. These features make it much more 
desirable than the common wire nail. 

The roofing nail (Figure 31) is not recommended. 
While the shaft is of proper thickness, its head is too 
small. 

The cut nail (Figure 32) is made from sheets and is 
of quite different shape than any of those made of wire. 
The enlargement of the shaft gives it more stiffness than 
the wire nail has, but there is some danger of splitting the 
slate if too large a nail is used. 

The following tables of slating nail sizes will be found 
useful in estimating or specifying: 


‘““Copperweld”’ Slating Nails 


c Diameter Nails Lb. 
Size Length Inches fackes (Mppee) 
2d 1 .102 386 

3d 1% 114 ZaAl\at 
4d 1% 128 176 

5d 134 ar28 133 
6d 2 144 87 


Copper Wire Slating Nails 


Length Gage No. per_lb.* 

i% 1p 303 
il ip 270 
1% 10 144 
1% 11 196 
14% 12 231 
1% 10 134 
1% 1 210 
13; 10 112 
2 10 104 
2% 8 46 


*Add 5% to above for Brass Nails. 


Cut Copper Slating Nails 


Length Weight | No. per lb. Length Weight 
1 2d 2% 8d 
14% 3d 190 234 9d 
14% 4d 135 3 10d 
134 5d 100 34% 12d 
2 6d 
244 7d 

Cut Brass Nails 

No. per Lb. 
Length Weight 
Slating Roofing 
1% 172 
1% 3d 164 
Ly, 144 
1% 4d 140 216 
134 5d 108 172 
2 6d 88 132 
24 7d 80 
24% 8d 64 IAs 
2% 9d 52 
3) 10d 48 75 
3% 16d 66 
Cut Yellow-Metal Slating Nails 
(60-40 mixture) 
Length Weight No. per Lb. 
14 3d 154 
1% Ad 140 


An Up-to-date Photo of a Crude Old Slate Date. A more 
precise design worked out in two colors of slate may 
provide permanent roof markings for aviators. 


26 


HE materials commonly used for flashings are cop- 
per, tin, lead, galvanized iron and zinc. Flashing 
materials should be selected with the same care as the 
The 


used 


other materials entering into the roof construction. 
When 


with a material as permanent as slate, it is, of course, 


first consideration should be durability. 


poor economy to use any but the most permanent and 
non-ferrous metals and the best workmanship. 


Copper 

Copper is peculiarly suitable for all flashings (inclu- 
ding valleys) as it is easily worked and shaped and 
adjusts itself to temperature stresses. Copper sheet is 
made in a wide range of weights and thicknesses and in 
what is known as soft or “Roofing Temper” copper and 
hard or “Cornice Temper” copper. Soft copper only 
should be used for flashings. It is generally defined by 
the ounce weight per square foot; that is, “l6-ounce cop- 


per” 
pound per square foot. 
be rolled from copper conforming to the Standard Speci- 
fications of the American Society for Testing Materials. 
Sixteen-ounce copper sheet is the minimum weight 
that should be used for flashings of any kind. Many 
architects will specify nothing lighter than 18-ounce 
material, and with the best work, where heavy sheets are 
used, 20-ounce metal is recommended as better practice. 
Flashings lighter than 16-ounce are undesirable. All 
rain water carries with it off the roof dust and grit which 
It is well to use 


means copper sheet weighing 16 ounces or one 
All copper sheets used should 


have some erosive effect on the metal. 
metal thick enough to do the work of carrying away the 
water for a period of time at least as long as the life of 
the building. Sixteen-ounce copper will meet such condi- 
tions; 14-ounce is too light. 

The following table will be found of value in specify- 
ing the weight of sheet copper. Copper for flashings 
should always be specified by weight and never by gauge. 


Nearest Gauge 
Weight Thickness arate 
Oz. Sq. Ft. Inch 
eee ries B.&S8. | Stubbs | U.S 
24 . 0324 20 PA 22\I 
20 .0270 Alt ide 23 
18 . 0243 Dap 24 24 
16 0216 ES 25 25 


RCP ORES AISA SESRSENEEEEE 


27 


%, a 


Pace i 


Copper sheets may be obtained in widths from 6” to 
108” and in lengths from 6” to 200”. Roll or strip copper 
is made in widths from 2” to 20” and in rolls of 75’ or 
strips from 6’ to 10’ long. Sheets from 24” to 42” wide 
and from 60” to 96” long are in general use in the sheet 
metal trade and are carried in stock. All specifications 
and details should be drawn with these sizes in mind. 

The edges of all copper flashings to’ be soldered must 
be tinned 114” on both sides and the seams thoroughly 
sweated with solder. Proper care in making the seams 
tight is of utmost importance. Use pieces up to 96” in 
length, and except on steep slopes (15° or over), lock 
and solder all base flashings. Cap or counter flashings 
need not be soldered. The joint is made by lapping the 
sheets in the direction of the flow. When there is any 
likelihood of deep, wet snow packing in or of wind lift- 
ing the cap flashings, the joints should be soldered, using 
either locked or lapped seams. 

All exposed edges of flashings—such as the bottom 
edge of cap flashings—should have a 14” fold back under 
for stiffness against wind action. This is a practice that 
should be axiomatic with good flashing. 

Copper requires no painting or other treatment unless 
it is desired to hasten the development of the natural 
green patina. In this case it is absolutely necessary that 
all the grease and oil used in the manufacturing process 
A strong soda solution 


A 


uniform finish will not be obtained unless the copper is 


be removed from the copper. 
(4 to 6 ounces per gallon of hot water) will do this. 


thoroughly cleaned. 

Copper can be painted provided the surface be thor- 
oughly cleaned and roughened. This can be done by 
washing the copper with a solution of 4 ounces of copper 
sulphate in 4 gallon of lukewarm water in a glass or 
earthen vessel, to which has been added 14 ounce of 
nitric acid. Before painting, the surface must be care- 
fully washed with clean water to remove the last trace of 
the solution. For additional data regarding coloring 
copper, refer to Part 3 of “Copper Flashings,” of the 
Copper and Brass Research Association, or write that 
association direct at 25 Broadway, New York City. 


Tin 
Tin used for flashings is more properly known as 
“Terne-Plate.” The base is of iron or steel and the coat- 


Sele Ee REO Oak ts 


ing a mixture of lead and tin put on the sheet by the 
hand-dipped process or Patent-roller process. The base 
metal recommended for flashings is the IX thickness, 
weighing about 6214 pounds per 100 square feet, or from 
250 to 260 pounds per box of 112 sheets size 20” x 28”. 
The lighter weight, or IC thickness, may be used but is 
seldom satisfactory. The weight of the base gives body 
to the metal, but its enduring qualities depend mainly 
upon the weight and thoroughness of the surface coating. 
Heavy coated tin will weigh from 290 to 300 pounds, or 
represent about 40 pounds of coating. While tin is sold 
in sheets of various sizes from 10” x 14” to 20” x 28”, the 
two sizes in more common use are 14” x 20” and 20” x 
28”. IX tin is approximately 28 gauge (U.S. standard) 
IC tin is 
30 gauge and weighs about 10 ounces per square foot. 

All joints should be securely locked and joints and 
seams thoroughly sweated with solder. 


and averages about 12 ounces per square foot. 


Tin should always be thoroughly painted one coat on 
the under side before laying, and all grease and dirt 
cleaned off, and then painted one coat on the top side 
after laying. Particular attention should be paid to this 
under-side coat and a heavy coat applied, as this pro- 
tects the flashings from the effects of condensation. 
Metallic brown, Venetian red, red oxide or red lead may 
be used, mixed with pure linseed oil. No turpentine or 
dryer should be added. A second coat should be applied 
to the surface two weeks after the first coat. One or two 
additional coats may then be applied to obtain the desired 
surface color. Tin flashings should be gone over, re- 


Where 


dirt or leaves lodge and are retained on the flashings, it 


paired and repainted about every three years. 


is advisable to remove any such accumulations and re- 
paint at yearly intervals. Proper maintenance will add 


immeasurably to their life. 


Lead 


The use of lead for building purposes is not new, and 
it is frequently very desirable for flashings. It is un- 
affected by ordinary atmospheric conditions and its soft- 
ness, pliability and malleability make it especially. valu- 
able in places where other materials cannot be easily 
introduced. Until the introduction of hardlead, the only 
lead available was soft lead, which, while possessing 
many excellent qualities, was impractical for flashing 
because of its low physical strength. Hardlead has a 
much greater tensile strength which permits its use in 
comparatively thin sheets. Lead is protected by nature 
through oxidation of the surface upon exposure, and 
requires no further treatment. 


Hardlead is rolled in sheets 24”, 30” and 36” wide and 


96” long, weighing 214, 3, 4, 6 and 8 pounds per square 


28 


foot. With respect to the proper weight of hardlead 
sheets to be used, one manufacturer states that this de- 
pends upon the purpose, and adds: 

“For gutter linings, cornice coverings, base flashings 
and roofing purposes generally, the 3-pound sheet is rec- 
ommended, and for cap flashings and batten roofs where 
the battens are spaced 18” or less on centers, the 214- 
pound sheet may be used.” 


The lead should be so installed that it can expand and 
contract, and nailing directly through the sheet should 
never be permitted. The sheets should be fastened by 
means of cleats. These cleats should be made of 16- 
ounce soft rolled copper or 3-pound hardlead, fastened 
to woodwork with two hard copper wire nails and to 
masonry with brass screws and lead shields. The cleats 
should be spaced about 8” on centers, but on steep roofs 
continuous cleats for the horizontal joints are recom- 
mended. 


Where the edge of the metal is fastened by means of 
a reglet, there should be a continuous cleat of 3-pound 
hardlead caulked into the reglet and the sheet should be 
locked to the reglet. Never caulk the sheet into the 
reclet. 

Where the edge of the metal is unfastened, such as cap 
flashings and similar conditions where a lapped joint is 
provided, the free edge of the metal should be hemmed 
about 14”. 


All nails should be hard copper wire flat-head nails 
not less than 34” long. All screws should be of brass 
and all shields of lead; iron or steel nails and screws, 
coated or uncoated, should not be used. The sheets 
should be joined together by means of locked seams. 
Lapped and soldered seams are not recommended. 
Wooden tools should always be used in working and 
beating the material into place. 


Zinc 

Zinc for roofing and general sheet metal work has been 
used in Europe for more than a century, where its perma- 
nence and freedom from repairs have been thoroughly 
proven. Its use in this country, while of more recent 


years, has shown similar results. 


Zinc is a metal, not an alloy of other metals, which is 
extremely resistant to the corrosive action of the ele- 
ments. It rapidly acquires a protective coating (a basic 
carbonate of zinc), which will continue to form as long 
as there is any raw zinc exposed. This protective coat- 
ing gives the metal a light battleship grey color which 
will deepen with age and approach the color of grey 
slate. Zinc does not need paint as a protection, but paint 
can be readily used if other than the natural color of 


FLASHINGS TO BE WOWEN INTO SLATE 

COURSES-EACH FLASHING SHEET TOLAP ff, 

THE NEXT LOWER ATLEAST TWOUMTIES ; 
\ 


COURSES AND E: 
VE UNDER CAP FLA SH- 
ING ATLEAST FOUR 


ly 


a 
Sy i ~ / 
g Yes 
YY 3_/ <> 


\ 
YA 
« 
Z 


BUILT IN BASE FLASHING OR DORMER LULA BASE TEAS IINGS OR CHTINEY 


W/NDOW ON SLATE ROOF | Oi DROPS On SaA/, LAO, 


COPPER COVERED CRICKET- COPPER EXTENOS 
VP VNDER SLATE ATLEAST SIX INCHES 
COPPER TURNED VP AGAINST CHIMNEY AND 
COUNTER FLASHED 


CAP FLASHING S 
ATLEAST 
2 INCHES 
1 SLATE TOLAP ie ie 
| OPPER AT LEAST Me ; f E CAP PLASHING 


FLASIING [OR CINMNEY ON SLOPE, FLASHING [OP CIVMINE Y ON RIDG 
O@rOLATE. ROOF Caan eA OOF 


FIGURE 34. STANDARD DETAILS FLASHINGS—NATIONAL SLATE ASSOCIATION 
Tl Ss form to t Stand search Association 


nese and all flashing details conform to the Standards of the Copper and Brass Re 


Sela Ee aheOTORE 


zinc is desired. The Association will be glad to furnish 
specifications for the painting of zinc upon request. 
Rolled zinc for flashings should be not less than No. 
11 zine gauge (0.024” thick) and should be laid in the 
usual manner, not nailed, but held in place by means of 
zinc clips or cleats. Zine flashing against masonry, 
concrete and stucco should be laid on a good grade of 
water-proof sheathing paper. If the cap flashing is set 


in a reglet, it should be pointed with elastic cement. 


Solder 


The agent used to join pieces of metal into one length 
or sheet is known as “solder.” The best grade, composed 
of equal parts of new tin and new lead, should be used 
and should conform to the “Standard Specifications for 
Solder Metal,” Serial Designation B-32-21, American 
Society for Testing Materials. To hasten its melting and 


conserve the heat in the solder iron, a flux is used. 


bL/INDS 

WOOD SILL 

COPPER FLASHING 7O 
EXTENO UNDER SILL 
AND LAP SLATE AT 

LEAST FOUR INCHES 


SLATE 


SLATE JS/D/ING—p> 


A COPPER FLASHING HELD 
|) 4Y COPPER NAILS 


FLASHING FOR DORMER 
WINDOW S/LL 


ai 


FLASHING FOR WOOD WINDOW HEAD 


Figure 35 


On copper, rosin is the best agent for this purpose, and 
the use of acid as a substitute should be avoided when- 
Acid flux of an improper kind may do 
irreparable damage to the finest workmanship. Rosin 
is harmless to the metal and makes good seams. There 
are some objections to its use, such as sloping roofs and 
windy days. Under these conditions it is much easier to 
use killed acid for it will not blow away although it may 
run down a slope and spatter on windy days. Rosin 
can be kept in place by “burning” it on with a small 
soldering copper just hot enough to melt the rosin. The 
proper preparation of acid for use as a flux is of great- 
est importance. The acid is hydrochloric or muriatic. 
Pieces of zinc are put in the quantity to be used until it 
stops working; then it is properly killed. If the kill- 
ing is done hastily or by any one not familiar with the 
procedure, the acid may be used in a still active state 
and attack the copper. The acid to be used for the entire 
job should be prepared several days before the work 
starts and allowed to stand. On zinc and galvanized 
metal, acid should be used. Where the joints of the metal 
are not thoroughly sweated or soaked with solder, they 
may be loosened by expansion or contraction of the metal 


ever possible. 


30 


or leave small holes in the joint through which moisture 
readily finds its way. 

A new product known as soldering salts may also be 
used as a flux. It is claimed that these salts do not 
require so hot a soldering iron and that they also have 


other advantages. 


LLL GLEE 


OHLPY LSE ATLL , 
£2 
4 / 
; j 


Le 


OEE Aap) 


~ 


SS 
aa pe 
STRIP. Si 


oeip —/ f 
COOP AGAINST SL OTE 
FLASHING [OR WOOD WATE? TABLE OR CLAPBOARD WALL 


Figure 36 
Galvanic Action 


Dissimilar metals, when in contact in the presence of 
an electrolyte, set up galvanic action which results in the 
deterioration of the most electropositive metal. 

Any possibility of galvanic action between copper and 
iron or steel should be carefully avoided by proper insu- 
lation. This insulation is effected in various ways, three 
of which are: (1) covering the steel member with asbes- 
tos, as is frequently done in skylight construction; 
(2) placing strips of sheet lead between the two metals, 
as when new copper gutters are placed in old iron hang- 
ers; and (3) heavily tinning the iron, as is often done 
with iron or steel gutter and leader supports. 


Flashings—General 


Flashing should be used at all intersections of vertical 
or projecting surfaces through the roof or against which 
the roof abutts, such as walls, parapets, dormers, sides 
of chimneys, etc. Flashings used over or under the roof 
covering and turned up on the vertical surface are known 
as “base flashings.” Metal built into the vertical surface 
and bent down over the base flashing is termed a “cap 


flashing” or “counter flashing.” 


Base Flashings 


The base flashings should be extended under the upper- 
most row the full depth of the slate or at least 4” over 
the slate immediately below the metal. The vertical leg 
must be turned up not less than 4” and preferably 8” on 
the abutting surface. Where a vertical surface butts 
against the roof slope, it is necessary to build in the base 


INGA Lele OsNir As 


See bee onoe O2Cr Loan ON 


CL EAT- 


SOLOERED LAP SEA/Y 
| LOCK SLAM SECURED TO 
ROOF WITH CLEATS 


i 
| COPPER NAILS JO SECURE FLASHING 


BUILT-UP ROOFING 


SLASHING TOR EDGE OF COMPOSITION DECK 


KOOF ABOVE A SLOPING SLATE ROOF 


TWO-/LY ROOFING WER FLASHING 


a 


— COPPER FLASHING AND GRAVEL STOP- 


STONE, CONCRETE, 
OR TERRA COTTA 
COPING 


COPPER CAPFLASHING- 


tae eer JO EXTEND THROUGH 
BRICK WORK AND LA, 
ROOK SHLATH ING STONE ONE /NCH 


weal 
u Y 


FLASHING [OR A BRICK PARAPLT 
WALL [ACED WITH STONE 


Figure 37 


31 


Sf a 


When a parapet wall 
is flashed on the top 
and back with metal, 
the flashing should be 
carried over and down 
to within one inch of 
bottom of cap flash- 
ing formed as _ here 
shown, so that most of 
the water is deflected 
out onto the slate. 


StLeAsT rE 


RIOCOsETS 


COPPER FLASHING TO LAP COPPER VENTILATOR 


SLATE FROM 670 8/NCHES 
AND BE FORMED OVLR <a e, 
see i Say 


Ae) 


FLASHING OR VENTILATOR ON SLOPE 
OF SLATE ROOF 


THREADED W.ACAP. 


SE COPPER CUT AWAY 


SLOPE Or, S04 | [aa O Omer 


COPPER VENTILATOR 
AND BASE 


BRASS WOOD 
SCREWS AND 
WASHERS 


SOR SECTION A-A 
Slee IC, Ht 


COPPER FLASHING 
TO LAP SLATE 
STROM @ TO 8 INCHES 
AND BL PORMED OVER 
SLA TELS 


SLASHING [OR VENT/LATOR ON RIDGE 
Of OLA iia Oo Om 
THREADED W-/-CAP 
COPPER FLASHING SLLLVE: 
LAP SEAT SOLDERED 


70 SHOW VENT AND 
ROOF BOARDS 


fey 


FLASHING FOR A VENT PIPE (4) 
THRU A SLOPING SLATE ROOF 


Figure 38 


flashing with each course of slate as laid. Turn out 4” on 
the slate and at least 8” above the roof. If the roof stops 
against a stuccoed wall, a wood strip 4” wide having a 
beveled top edge should be secured to the wall. The 
base flashing is then turned out over the slate at least 4” 
and bent up vertically at least 3” on the board. Except 
in unusual cases, it will be found satisfactory to turn the 
base flashing out 4” on the roof surface and up on the 
vertical surface from 6” to 8” for either sloping or flat 
roofs. Posts, flagpoles, scuttles, etc., where projecting 
through the roof, should have base flashings. Vent pipes 


should have base flashings in the form of special sleeves 
or one of the numerous patented roof flashing devices. 


Cap Flashings 

Where the base flashing is not covered by vertical slate, 
siding, etc., a cap flashing must be used. This member 
should be built into the masonry joints not less than 2”, 
extend down over the base flashing 4”, and the edge bent 
back and up 14”. Reglets in stone or concrete are usu- 
ally about 1” wide and 1” deep. The flashing should be 
formed and laid in the bottom of the cut and thoroughly 


32 


Ne Ace OS NGAS I 


Sr let econo Ose JAS Tl LO UN 


a 


caulked with molten lead on flat surfaces or lead wool on 
upright work. After caulking, the reglet is filled to the 
surface with elastic cement. Flashing hooks should be 
used to secure stepped flashings and the vertical legs be 
made tight with roofers’ cement colored the same as the 
masonry. On the best work these flashings should be 
soldered. 

Tt will be noted on the drawings that all exposed and 
unfastened flashings have the edge of the strip turned 
under 14”. This is done to give the strip stiffness against 
wind. Thus the sheet is held in place and the packing in 
of snow under the flashing is prevented. 


Saddles or Crickets 


Where a chimney or other vertical surface breaks 
through the roof at a right angle to the slope, a saddle 
or cricket must be built to throw the water away from 
the back of the vertical member. If the roof construc- 
tion is of wood, use light rafter construction covered with 
sheathing boards, paper and sheet metal. If of very 
large area and exposed to prominent view, it should be 
slated the same as the other roof areas. Valleys will be 
formed with the main roof and it is recommended that 
they be of the open type. The size of the saddle is largely 
determined by the roof condition. It is usually sufficient 
to make the slope of the saddle the same as the roof. 

It is most important that the saddle or cricket be of 
adequate size, of ample slope and well flashed as shown 
in Figure 34. 


Estimating Flashings 

In case it is desired to estimate the amount of metal 
required for flashing mitred hips (where metal is used), 
closed valleys, cheeks or side walls and base and cap 
flashings for walls, the following rules used by one roof- 


ing contractor may prove of value. This rule considers 
that flashings for hips and valleys are bent diagonally 
from corner to corner, while those for cheek or side walls 
are bent lengthways, allowing 4” to turn up on the side 
wall and 4” flashed under the slates. 


RULE FOR ESTIMATING FLASHING 


for Mitred Hips, Closed Valleys, Cheeks or Side Walls 
and Walls. 


Hip and Valley Slip Flashings 
Multiply the number of lineal feet of mitred hips and 
closed valleys by the following percentages, and the re- 
sult will be the number of square feet of sheet metal for 
flashings, using slips. 


Size of Slates Size of Slips Multiply by 


12” 9x 9 800 
14” 10 x 10 825 
16” lit ie 858 
18” 12x 12 908 
20" 13x 13 946 


Cheek or Side Wall Flashings 


Size of Slates Size of Slips Multiplied by 


12” 8x 7% imbal 
14” 8x 8% 1.031 
16” 8x 9% 975 
18” 8x 10% 934, 
20" 8x11 902 


Wall Flashings 
Multiply the number of lineal feet by 1.1, and it will 
give the number of square feet if flashings are 12” wide. 
If courses in valleys do not line up, it will require 
double the number of slips to flash properly. 


-T has sometimes been stated that heavier roof construc- 
tion is required for slate than for roofs of somewhat 


lighter materials. This is not true—that is, when slate 
of the commercial standard thickness is used. Such slate 
comprises the vast majority of all slate used for roofing. 
Obviously, for a graduated slate roof, where very thick 
slate is specified, the roof construction should be designed 
to provide for the increased weight of the slate. But for 
the regular or standard slate roof, any roof construction 
which conforms to good engineering practice, and is suit- 
able for other roofing material, is adequate. This fact 
should be fully recognized in the interest of truth, econ- 
omy and conservation. The weight of the roof covering 
is an insignificant quantity when compared with the com- 
bined weights of rafters, sheathing, snow and wind pres- 
sure which must be considered for all roofs, and water 
saturation of certain roofings other than slate. 

The allowances for the combined snow and wind load 
on roofs is usually established by local building codes 
or custom and will naturally be found to vary in different 
sections of the country. Certain localities are subject to 
higher winds or heavier snowfalls, or both, than others. 
This anticipated load is several times the combined 
weights of the materials which make up the roof con- 
struction and covering. 

Building codes usually specify requirements for the 
live load; that is, any load other than the weight of the 
construction itself, such as snow, wind, etc., which must 
be figured for all flat and sloping roofs. The average 
for flat roofs (less than 20° slope), taken from the codes 
of fifteen representative cities, is 40 pounds per square 
foot. For roofs of more than 20° slope, this require- 
ment averages 30 pounds per square foot. 
The dead load of the roof 
construction consists of the 
rafters, sheathing, or roof 
lath, the roof covering, and 
plastering on under side 
of rafters when it occurs. 
Rafters, depending upon size, 
spacing and kind of wood, 
may vary from 1 to5 pounds 
per square foot of roof 
area. Sheathing boards will 
weigh about 214 pounds 


and roof lath from 114 to 1144 pounds per square foot. 

The roof covering may vary from 1 pound per square 
foot for three-ply ready roofing to 14 pounds for clay 
tile shingles. Wooden shingles, dry on the roof, average 
21% pounds per square foot. Slate of commercial stand- 
ard thickness, dry or wet, will average 7 pounds per 
square foot when laid. 

To demonstrate that standard thickness slate does not 
require heavier roof construction than is necessary for 
other roof coverings, the following comparison has been 
made, based on a typical roof: 


Wood Shingle Standard Slate 

Lbs. Lbs. 

Roof Covering....... 2h) e0 

Sheathing aera hI) 2. 

Watters. eee a: 3.0 3.0 

Deadtlioadieenenre 8.0 1173.5) 
Average Live Load 

required by law... . 40.0 40.0 

48.0 5 


Engineering calculations for the same roof conditions 
show that on this slight difference in weight, rafters of 
commercial stock size dictated by good practice for 
lighter materials will be of strength amply sufficient to 
accommodate standard (3/16") _ slate, 
whether on a new roof or for re-roofing purposes. 


commercial 


Figure 39. Parts of Roof Construction 


Ne Nee ORNGs log be Ag ater Anoo.0) CloAT TT IO -N 


HANDY RAFTER TABLES 


The following tables provide a handy means of determining the size of roof rafters for any slope, uniformly 
loaded, for given spans in feet, and rafter spacings measured in inches from center to center. 

Tables of sizes are based on the dead load, which includes the weight of the rafter, weight of sheathing (2.5 pounds 
per square foot) and weight of roof covering (8 pounds per square foot) and live loads of 50 and 30 pounds per 
square foot of roof surface considered as acting normal to the surface. 

Where the ceilings are covered with some hard, inelastic material such as plaster, the span lengths should be 
limited by the deflection to prevent cracks. Where the ceilings are not so covered and where a small amount of sag 
or spring is not objectionable, the span length may be determined by the bending strength of the member instead of 
by its stiffness. 

Allowable stresses for timber are usually prescribed in local building codes, but when they are not it is recom- 
mended that the values given in Table No. 4 be used. These values are taken from the recommendations of the Forest 
Products Laboratory, Department of Agriculture, at Madison, Wisconsin, that were officially adopted by the American 
Society for Testing Materials and the American Railway Engineering Association. 

The following tables are compiled from “Wood Construction Information” issued September 1, 1922, by the 
National Lumber Manufacturers’ Association. 

TABLE No. 4.—Allowable Unit Stresses for Structural Timber 
(Pounds per square inch) 
Do not use this table if local Building Code specifies timber stresses. 


Modulus of Stress in 
Species of Timber Elasticity (E) Extreme Fiber (f) 
(For determination | (For determination 
of Deflection) of Bending) 
(Cedar Viesternsliedered aac eat ee Ath eg hey wir Alera OW! CO SR Wes me een sates concep, ay ued es 1,000,000 900 
(CHAE I ORT Rs cca % Ets sete <eechey a BRR Oe AS GEIS ME NDR NE) Pah Seen OE i een ee ee 1,000,000 950 
(EN DESS MRE RTT NE arte ates ee Ae a ge hes ta ANAT ONO Ot A eye Wk ap 1,400,000 1,300 
Douglas HiniNowkstruc tty ee ete eee ee Sie orn ee eer cece ae nee 1,600,000 1,600 
Donglasmhira (Nos opo Uru CUS) eyed crak ie ea ee aan ee A te the a eben siti pun Ma dela g) Nthcts 1,500,000 1,300 
Dyas hiss [ie Tore ay IM Karri INGA. ou ogauns oe coo dhoewonupoonons bopoobkcnednodec 1,200,000 1,100 
ET eeLs ALS ArT ere ee ei ee re ee tee a cen REO BoD her AiR nate Mee aed ane aliens Bh 1,000,000 900 
(Cronin, LEYS, ee Soe ee Geeky RRB fo aa ck Shcsen th eacuceee MAUR eee ei, Mrtei-Pi aRPIN eb SNe OP eae er Sn ee rere ee eae 1,200,000 1,100 
Fe mIlOGKae Vics teria tere lt ey aes tire) nen Stes pat Sean tv Ne dn Bl A a 1,400,000 1,300 
EVemlO CK BEas Cer iice eee eae cee eae ee re ne eke tee a 7 LA Te Benes gah. Si ae 1,100,000 1,000 
EAR CHER VCS CELTIC Sree eee oat Ree Rain, AE MENTE tes Pot i we Rey Oe s BAR dass 1,300,000 1,200 
Maples Supar ort rlard seme tires cctre ar te ne Sere re ae ie Ae SOE tt ray ees, AENNC eee a Oe 1,600,000 1,500 
IVa pl emoihy CHIOLE SOL Gree eR NT Ha ORR eects ak ee OS ih Soe oo te at aac 1,100,000 1,000 
DalAeVWV hi ero edt eee ae eee Bie gm tery oa toe taw Wer Choe Peds Oe OE 55 y 1,500,000 1,400 
Pinemooucherney ellows (Dense) ewer orn ere en Serene a en Ce ae AC nee Ae oa, 1,600,000 1,600 
Rinewooutherney ello wal( SOUT) kerma teen: Mnm pain ery e Mee ug Poh yt yes ess 8 a 1,500,000 1,300 
Rinewasterne items weer ee Geer ar eee ee eee Pe Py lene eB ahr Nghe A eg 1,000,000 900 
ime Wiesteriney VECO ec ror eee eee cote cr ter EOS CoD Nee, Src ata dae tin oe ee 1,000,000 900 
Ie NOL WAV eer er ean Eiciaroo ea eg Tete Sie Re Re ees oe Wee Se Naan emia on, BS re 1,200,000 1,100 
VEC WOO Cee meen eet a tye UE re: a5 SPEER atk Soe MUM. wth Mr en Bale aati gs Sok IMAM ee 1,300,000 1,200 
SDLuce secon WaniterOnsolt kale games oy wpe me ec een ee. REE Ree NE coh es oe 1,200,000 1,100 
TRENTO TREY] ed BENSTIG) ge Ga ee eens nh cutout, ed neh en ek RN So nl, BE ee gw Oe ne a ee 1,300,000 1,200 


TABLE No. 5. 


Order of Strength of Standard Sizes of Rafters as Determined by their Modulus of Elasticity (E) and 
their Extreme Fiber Stress (f) in Pounds per square inch. 


Deflection (E) Bending (f) 
De ah 2x 4 
2x 6 5% 
3x 6 Bye 6) 
2 ER oe 
Boxe Qexal0) 
Dsxell() 3x 8 
3x 10 2x 12 
Poe \e OPO 
Boe 1 2x 14 
2x 14 33 a6 1 
SoA 3 x 14 


39 


DeLeAG Ey eheOsOetes 


SS .....__2222....—in 


TABLE No. 6.—Rafter Sizes for Roof of any Slope—Uniformly Loaded 


Based on Modulus of Elasticity (E) and Limited by a Deflection of 1/360 of the Span. 
Live Load—50 pounds per square foot. oy 


(Use the following table when the roof is desired to be very rigid in order to prevent cracks in plaster or other inelastic material 
on the ceiling.) Use Modulus of Elasticity (E) given in building code—if not given in code use value for E for kind of wood used 


in table No. 4. 


Size of Rafters (Nominal) in Inches 
Span Between Plate and Rafter Spacing 
Ridge or Supporting Center to Center 
Members in Feet in Inches E =1,000,000 E=1,200,000 E=1,400,000 E =1,600,000 
12 2G DG 26 ee a 
(COA aestS SRM Piss Rent i den ik ON SG Al 16 22X16 2X 6 2x6 Bx G 
24 Zixemn Bore 6 Bx O 726 
12 2% 6 eG 2x06 nce eee 
RET p, ROMR oe TT See rere re aor tr, PR eon 16 Boxe 6 Xan De (5) 2 xe 6 
24 Bo Sx C Sox EC Be 83 
ie 12 2x 8 Bad 256 3x 6 
HU Pe ere ov cg des Wr ce A NS RO oS od 16 2x8 2xo XO 3x 6 
24 Boe £03 Xan) 38 2 xXaanG 
1/22 ae 8 xe 8 We §R Be 83 
ae IF a aCe ae ae oes AN ae, Seeks Ue RPE SPE 16 256 AMY) See 3 aoe ft ayo 8 
24 Sexe iO Sexa() Zaexan() Boe 
(2? 226 1D) 72 Xe MO) Boxe Bye 883 
LAD re cert he rd ac ay or ran wae ty 2 oe 16 SO Ee 124 Dexa) xa) 
24 Sy xe LY 3x 10 By xe 10) Boe 1K) 
ip ox LO By xe UY) 3x 10 2 MY) 
I CR eee era? Ute ROMER CR IRaeE ete  Sok ent Barner Aiereetnsen 16 3) 6 Pe Boxe 10) Sexell() 3x 10 
24 SExLZ, 2x 14 Sexe Roe WY 
mee 12 3x12 3x12 3 x 10 3 x 10 
OES eee a Aine eI ee ee 16 3h 5% 12 Sex 33 xe UY Dexa, 
24 3x 14 3x 14 2x 14 Sypre 1 
ae 2 Dx B xe A 83 xe UH SoxaZ 
7 Ve I ton SE I eh BO ere a rie tn AS eRe 16 xe 14! 3x14 Syne 1 By oe hy 
24, ae ce 3x 14 3) xe 14! 
ao 12 ar 3x 14 2x14 2x14 
DRE erg Fen Esty eel act en EAA ee Pe 16 wee Be IAL 3x 14 Se U4) 
meh 12 3x 14 3x 14 3x14 
PAL NAO BS UPA WON Sera Ar OUR Ais Mineo Wein eas APE Rad 16 aces 3x 14 
24 a 


Nore:—Ltve Loap =50 lbs. per square foot considered as acting normal to surface. 


Deap Loap=weight of roof joist. 


weight of sheathing (2.5 pounds per square foot). 
weight of covering (8 pounds per square foot). 


36 


Nee eels eOe New eto LaAg he Eee Ae S75: O GT AR TO 


TABLE No. 7.—Rafter Sizes for Roof of any Slope—Uniformly Loaded. 


Based on Extreme Fiber Stress (f) 
Live Load—50 pounds per square foot. 


(Use the following table when a small amount of sag or spring does not matter. Use Extreme Fiber Stress (f) given in local build- 
ing code—if not given in code, use value for (f) for kind of wood used in Table 4.) 


Span Between Plate ; Size of Rafters (Nominal) in Inches 
and Ridge or Sup- | Rafter Spacing 
porting Members Center to Center 
in Feet in Inches f=900 | £=1000 | f£=1100 | f=1200 | f=1300 | f=1400 | f=1500 | f=1600 | £=1700 | f=1800 
ho 12 dG Pose all A Ge || aa are el ea 
Ge ea te C5 Re 16 Dse © | Moe Gl Bx O |] Boe G || Soe Gl Bee @ | Vse Hl] Mee w |) ae yl Bre G 
24 Dox Pex O 726) EXO) Axe Dexa © Ase (6 2X0) Xeno 2 XoL6 
12 Be 235% Boe 6) PAS (H) axe (6) exam O) 2x6) 2x6 exe) Zee O, 
ie, As he OR ee ee 16 3x 6 Woe eX lO Pee GS Be Xone O) > (8 PA 1H 2 Xa O) xa) 
24. SEXO 336 © Dx Hx G Rox O exe 0) Dexa) Be & Se 6 2x 6 
13 nO ae GO Re O ase @ 38 {8 Boe (6) Exe XE BSE xe Hee 16 
LOMpae rrr ete. 16 se | Bar GO |) Bax G |) See G I Boe G | Bae He Ase Gi se i |) Pree Gy I] Wee 6 
24 2x 10 xanli() 24 xe 10) 2x 10 Pao, ts) Dox © BS Boe © 3xe nO Bixee (6) 
12 De OR Rox G Bx Boxe Boxe Boe Doe Re (6 Bx DES (5) 
(eR Re es on Aten 16 Xe MY exau 2 MG Xa © Boxe C Box Dax EC Be 6) a6 2X 9S 
24, eXane xan ey Po xe AN) exe) 6 ANG xe LO 2x10 2x LO Dexwi() EXaG 
19? 7 SE AKY) BEM) 2x0 2x0 ExaenG DI Boe 1G 3x 6 Roe LO 
Ve Ree eA 3 3 o-ac Gee 16 Dexa xe te 2 xa 0 2x10 2x U0 Pee AKY) 2x 10 Pee 8 Pare fa 3x. 6 
24 aac IKW) Sexe) exe be 74, 3 1 exalt, P2356 1174 BMD Zea) PS AUD) Dexa LO) 
12 xa, Dexa 2 xoO Pees Kl) Bae ID) 2256 NG) Dexa PES 83 PIO £85 Dixe <C 
INGE G ce ee we 16 Boxe IK |) Boe 1 |) Bese IPR || Bess II |) ahok Bi Bie | Ae TIO) I Bese 1) i BS IK) |) Giselle 
24 Roe Ly 2 1a! exec 3 xo 10 sare 1G) Dexa le, exenley exenliy 73, 5 AVP Dx 12 
i xa, PES 112} aexenlie 2x 2 Zea) 2x0 2x 10 Zax () 2x 10 2x 10 
Geet tetents tatu: 16 2x 14 2x 14 axe Ip) 2x 12 25 Xe IP Dexa 7, 3&1 ae Dexa) exonli() 
24 ‘3x 14 3 x 14 a) ne 1 2x14 2x4 Dexa sx LO Spxee iC) POSS Ne Pee NP? 
1 2x 14 Sex 20 Dexa, exe Pb Se Ps Dexal2 DXoND, Zax Pes¢ AKY) Pee 1K 
2, ey ionee oes See 16 aioe Ihe 2x 14 2x14 ZX: 3x 10 sae 1) Paxenl Zax, Zax le, 2258 UY 
24 ay ae LA! 3x14 3x14 aye 3 ae 11 2 xe [el Zea 2x 14 Bie [lah 
1; 2x 14 exon 2x 14 33 xe 1) Se 1K) 2x 2 xe Pap ae Me 2x7 12 Dex 
ities che 16 3 re ab 3x 14 Boe 2x 14 2x 14 2oxe 14h exenlAi Be 1D) 3x 10 Pa Se 
24, Pen ae 3 x 14 3) 0% IAN 3x 14 SExe4 ae LY ay se 17 2x 14 
14 3x14 3x 12 2x 14 2x 14 ae 1 Here 10) aioe IK) Pee 14 PES A Dexa? 
CA 16 Seer 3x 14 3x 14 3x 14 Sexe le 2x 14 exe Al 2x14 xe De 1h 
24 3x 14 3x 14 3x14 3x 14 3x 14 


Note:—Live Loap =50 lbs. per square foot considered as acting normal to surface. 


Deav Loap=weight of roof joist. 
weight of sheathing (2.5 pounds per square foot). 
weight of covering (8 pounds per square foot). 


The Building Code Committee of the Department of Commerce, in “Minimum Live Loads Allowable for Use in 
Design of Buildings,” November 1, 1924, states regarding roof loads: 

“Roofs having a rise of 4 inches or less per foot of horizontal projection shall be proportioned for a vertical live 
load of 30 pounds per square foot of horizontal projection applied to any or all slopes. With a rise of more than 4 
inches and not more than 12 inches per foot, a vertical live load of 20 pounds on the horizontal projection shall be 
assumed. If the rise exceeds 12 inches per foot, no vertical live load need be assumed, but provision shall be made 
for a wind force acting normal to the roof surface (on one slope at a time) of 20 pounds per square foot of such surface. 
(See Appendix, par. 7.)” 

This Appendix paragraph reads: 

“The minimum roof loads specified in Part II, section 5, apply only in localities where snow loads are not an 
important consideration. Roofs having a slope of less than 4 inches per foot are always liable to accidental loading, 
such as groups of moving people, storage of material, etc. Hence the necessity of moderate unit loads even where snow 


Be 


Sabene Ee OLOek ss 


is not to be expected. Where large snow loads are to be anticipated, the loadings prescribed should be increased in 
accordance with local experience.” 

In view of these recommendations, the National Slate Association has deemed it advisable to include tables for a 
live load of 30 pounds per square foot, and these follow. 


TABLE No. 8.—Rafter Sizes for Roof of Any Slope—Uniformly Loaded. 
Based on Modulus of Elasticity (E) and Limited by a Deflection of 1/360 of the Span. 
Live Load—30 pounds per square foot. 
(Use the following table when the roof is desired to be very rigid in order to prevent cracks in plaster or other inelastic material 
on the ceiling.) Use Modulus of Elasticity (E) given in building code—if not given in code use value for E for 
kind of wood used in table No. 4. 


Size of Rafters (Nominal) in Inches. 
Span Between Plate and Rafter Spacing 
Ridge or Supporting Center to Center 
Members in Feet in Inches E=1,000,000 E=1,200,000 E=1,400,000 E=1,600,000 

1h Boe Ah 2A Bre Al moe Al 

(Ch aha Si Saint nhs 8 AU ei nh Nano A tec 16 Bos De & axel 2x A 
24 Moe O Be 6 axa se. (6) 

12 Bse 6 Bre (6) 3 2x 6 

Greer ele eet common rete cee tone macabre 16 Ase mse (H Wse (6) se 
24 axe se (0) 2X6 Boxe (6 

1 x 6 2X10 2x 216 BOE (6) 

LO Ee Sees a, Poe Chore aneeee 16 Dx & Boxe © oe Boe AG 
24, Xam EXO Axe 8 Ree 

1 xe $3 He (83 Bs G 3x96 

1 Aa era ewe I) ete, or ROR are ie Mastic mit 16 oe AB B xe (8 Me 3B Boe 
24 Dexal() Be & Boe £2 SOO 

12 Soe 03 3x 8 2x3 Boe 

VARNEY Bee Fs cree ye eI Cacao ee Lis eee is 16 2x10 oe. 8 Bee G xe 
24 8 3x 10 2x10 WS AN 

- 12 3x 10 2x 10 3x 8 3x 8 
Li: ca Re es oo el eae cs Se PRE OM S 16 3 xe IW 3x 10 256 1K) Boe NG 
24 See Dex 3x10 3x 10 

12 xa) 3 xe IC 3x 0 xO 

SS ed beeps pees hale, AE OME te eis AL ate coer ah 16 > xa Me 3x 10 3x 10 
24, Pap an 2 Bye 1127 38 UY ayo 1174 

ia 12 3x 12 2x12 3x 10 3x 10 

A Np. wh apathy Pk Ae SUN 3 Wn LR Eg eee SRae pec 16 Sax 112) 3) xe 1B B5e 11D) De 
24, 3x 14 Sexe lA: 35¢ 17 Boxe 

WP? 2x14 By sxe IPs Seall2 Boe MNP 

DO MA a Rene Soar rte Rca 16 3x 14 3x 14 3x12 3x12 
24 3x 14 Soe {ah 3x 14 

12 3x 14 3x14 35 xe 17 ay xe 11 

CON MAS ie ia aR er a, Bae <a cae aN INE CeCy RITES 16 aire 3x 14 3x 14 3x 14 
24 ae ae eee 3x 14 


Nore;—Live Loap =30 lbs. per square foot considered as acting normal to surface. 
~ Deap Loap=weight of roof joist. 
weight of sheathing (2.5 pounds per square foot). 
weight of covering (8.0 pounds per square foot). 


38 


Nea Og Ne Nate om cla ee Al oeo.O Gy lA Tl OrN 


TABLE No. 9.—Rafter Sizes for Roof of Any Slope—Uniformly Loaded. 
Based on Extreme Fiber Stress (f) 
Live Load—30 pounds per square foot. 
(Use the following table when a small amount of sag or spring does not matter. Use Extreme Fiber Stress (f) given in local 
building code—if not given in code, use value for (f) for kind of wood used in Table No. 4.) 


Span Between Plate Size of Rafters (Nominal) in Inches. 
and Ridge or Sup- | Rafter Spacing 
porting Members | Center to Center 
in Feet in Inches f£=900 | £=1000 | £=1100 | £=1200 | £=1300 | £=1400 | £=1500 | f=1600 | f=1700 | f=1800 
12 2 xe Al mo Al Bee ah Boe Al Pere Hl Dexa: se Ab Pie wh mse al Bee al 
(Edits EN eee eae 16 moe wh Moe ah Gx Gh | Bis% Al xe 2x 4 M5 AL Moe A | Woe Ab 2x 4 
24 2x 6 axe OH |) Bre C Boe B23 Al Ore Be |) Base el | Woe al Dexa 2x 4 
12 D5 (Hy | oe Dexa 6 2x 4 ree ah || Beye HE |) Piste al Pes dk |) Bise A) Dix A 
CURR Gs eas SP Gt 16 We TW i Boe |G ws. | Ase exe O Pex (6 BS AG Be Al TxA: 2 xo 
24 ax OG | Ase C Ose My || se 2x 6 se 6 exe O 2 xen 2 xaaG Dexan6 
12 Mose (6 mse OS | Base 6 BS O | Bs. 6 Be (GQ | Axe GH )) Ase Gy Bse Ol Ase 4 
LORS i. es 16 Be © 5% (i |) Se 45 H || Be O Boe MH | Bee Gy |) Boe xan 2 xa: 
24 Moe 3x 6 3x 6 3x 6 Roe O ase WH i) Moc Boxe Be exam) 
12 aac |) Bx © sxe | Bee (Hi) PPS Cpl) Bese Bre (% 2566 2x 6 Dxm6 
ME Sos Bk seine eee ame 16 Boxe ax © Boxe | 3x 356 axe Boe 6 2x 0 oe (0) 2ae6 
24 2x10 2x10 exenl\() Se tH) 2x3 Boe © Soe (0) 3 6 ore (6 3x 6 
12 Pe 83 Bx 6 Boxe O 3x 3x 6 Rise Wyse 6 2ExanO Me (GI Se 
Te or tk a eee ee 16 Bee) |} Boel | Bre ilO| Boe B | Sse GO |) Sse G | Boe G |) Sse Gi Bae G |) woe 
24 21 Wl Bae HB || Paste MO! fh Bese UM) |) Sse WD I) Boe 1K: || Bese TI We Base TI), |) Bese Te IP alse 
12 2x 10 2x 10 2x10 ae 3 aoe 3x 6 oben O Saxo se 3x 6 
NG Sats Beste ee ne 16 Soe 1B || AB xodld) |b Sse || Aes) ff Ase. | se iki || Mae BB |) Stor 8 |) aise KH |b Sie 
24 3) 2¢ IO) Zexae Zexale Zexal2 SEXaO ane <3 2x LO 74 Xe MY 2ExaLO 2x10 
12 exe LON a2 oxtkO exe () 2x 10 2 5% AND) Dexia () Dexe LG Boe (H B58 AG 3x -6 
Si) toe See es eee 16 Die (93 || Deore IBD Il BP ox BA || Prot TN |), Bisre TM ] Pe sc IK) || Base ik) |} pase i) |) Bese Ky iP sre 
24 Bee eh WP ese Tah |) adore IM |) Bae 1 | sre I || Pere IPA) |! Base 1b |) Baste ies Bese Ke th By oced I) 
1 Pale 12 98 SAWS 2a eExali() Poe 1) 25 € 110) 2x10 2x10 Pe Se ANY) 2exa 5 
ADE oh gece te ee 16 ase IO | Bixee) || Brcales |) Bisel | Broly Biss 3 il Base IK 4], tee aI) |) Based |) Pape I) 
24 aoe 1A || se ilah |) Bokeh |] ase dl Bisel {Bree IO | Bsa is | Bis Ibe I Base I se dip 
12 HR UO | Bs ie | Ao UW | Bsc ile shoe wb) Pyse Ti) || Sys TO) | prow WW || Bee TI) i Bese 1) 
OR Neo hci cehs 16 P58 Meh.) hore AN |) Bho 1D) || oe IPA) Pe TI | Oks TIO  OeGe Ie | ese || Bis GR a] oD 
24 Boe Mah | Sia day |) Soe il, Wl Bsc all: Il Base Tah) Wise idk | Bisel | ByoeI Rise Te |) paved 
12 Poe AIA) 8) xe 110) 74 50 APA Dexa, De 1 BS MB 745 1S an A) ee AMG 2x0 
Bee Noctis. Gls eae ee ene 16 Sine Ae | ese I | Basel | Base zy Shore 1). |) Bis TG) |! BAS Ibe Hl eee nOA I) Dasa Tip |) a'e 1174 
24 Arne B) oe 1A! Bie 1h 3x14 axe 1H 3) xe 1h 2x 14 2x14 2x14 2x14 


Nore:—Live Loap =30 lbs. per square foot considered as acting normal to surface. 
Deap Loap=weight of roof joist. 
weight of sheathing (2.5 pounds per square foot). 
weight of covering (8.0 pounds per square foot). 


It may also be pointed out that, although the wind pressure will remain the same for any roof no matter what the 
covering, Kidder’s Architects and Builders Pocketbook gives slate a snow load credit of from 3 to 12 pounds per 
square foot over shingles, depending upon the slope of the roof and the climate. 


39 


N any type of construction, it is important that the 
| ea Ge members be well tied together. This is espe- 
cially important in roof construction at the joint of the 
wall plate and rafter or a purlin and rafter. Ceiling 
joists or other horizontal members spiked to the foot of 
the rafters ordinarily accomplish this. In addition, the 
foot cut of the rafter should be so proportioned and de- 
signed that it will resist as much as possible the tendency 
o “slip” or spread as well as provide sufficient area to 
Good 
practice dictates that a wood plate on a masonry wall be 
bedded in mortar and securely anchored or bolted to the 
wall. It is needless to say that the walls receiving the 
roof load should be of sufficient strength and so built that 
the reactions of the roof and various floor loads will be 


prevent crushing of the rafter or plate fibers. 


kept well within or near the center of gravity of the wall. 
The footings should be properly proportioned to keep 
the load on the foundation within the soil bearing value. 

At the ridge it is advisable to use a ridge pole or 
board, rather than butting the peak ends of rafters of 
opposite slopes. The use of a board or pole affords 
better rafter bearing and will provide a straighter ridge. 
Collar beams spiked to the rafters near the peak assist 
in resisting the tendency to spread. If the simple prin- 
ciple of triangles used in truss design is followed in tying 
and bracing the structural members, a safe and economi- 
cal roof framing layout should result. 


Sheathing or Roof Boards 


Wood sheathing is commonly of tongued and grooved 
boards dressed on either one or both sides. If dressed 
The 
boards should be 1” nominal thickness (not less than 
25/32”) and from 6” to 10” wide. A width of 8” is a 
convenient average size and preferable to the 10” width. 
The tongue should be laid toward the ridge. Square- 
edge, rough boards, when used, should not be over 8” 
wide. Shiplap boards are preferred for sheathing by 
some roofers, who claim they have less tendency to warp 
than tongued and grooved when nailed too tightly to- 
gether. 

It is important that a smooth, solid job of sheathing 


on one side only, this side should be laid down. 


be obtained to allow proper laying of the slate. Joints 
between the ends of boards should occur over the rafters 
and the ends should be securely nailed at these points. 


40 


Lob eNe 


The boards should also be nailed with 10-penny nails at 
If 10” boards are used, it is 
advisable to also nail the center of the board to its bear- 
ing. Tongued and grooved boards should not be drawn 
up too close, as there is danger of the roof surface buck- 
ling if rained upon before the slate is laid. 

The tongued and grooved boards are generally to be 
recommended as offering a smooth surface and a tighter 
Square-edged boards 
are liable to warp and curl, and although this is seldom 


both edges to every rafter. 


and warmer roof than other types. 


sufficient to break the slate, it may raise the courses and 
mar the appearance of the roof. Uneveness of the sheath- 
ing surface invariably results in a noticeable uneveness 
in the roof surface. For this reason, scrap lumber, con- 
crete form lumber and pieces of uneven thickness should 
not be permitted as a covering for the rafters. Improp- 
erly nailed boards and loose joints make it difficult to 
lay the slate for the process of driving the slating nails 
into the sheathing springs and loosens the adjoining 
slate. 

Roof lath or strips 1” thick and 2” or 3” wide and with- 
out felt are used in many localities. The spacing of the 
lath will vary with the length of the slate used. The 
upper end of each slate should rest on the center of 
strip and the slate should be so punched that the nails 
will be driven into a lath. When the slate is laid with 


the standard 3” lap, the lath should be spaced as follows: 


Length of slate] Spacing of lath | Length of slate | Spacing of lath 
(Inches) (Inches) (Inches) (Inches) 
24 10% 16 6% 
22 914 14 51% 
20 814 12 416 
18 7% 


This method of supporting the slate will not provide 
the warmth and the resultant saving in heating costs of 
other methods. While suitable for barns and similar 
structures, it is not recommended for use upon residences 
and important buildings except under favorable climatic 
conditions. 


Round Valley Foundation 


The foundation for the round valley is part of the 
sheathing work. There are three methods which may be 


ING oe ORNGAS E 


SelipAgi ak gAt Ss OF; CaljAST TOON 


used. The first, suitable for valleys of slight curvature, 
consists of a wide board (usually 12”) made with taper- 
ing sides and nailed into the angle formed by the inter- 
secting roofs. 

In the second method, suitable for any curvature or 


Unusual Slate and Glass Roof Baseball Cage, Amherst College 


radius desired, 3” blocks cut to fit the valley angle and 
sawed to the proper radius are nailed over the roof sheath- 
ing and spaced approximately the same as the exposure of 
the slates. The blocks thus form nailing strips under 
the slate. The size of the blocks will vary, due to the 
diminishing size of the valley as it approaches the ridge. 

The third and usually the most satisfactory method is 
a combination of the first two. The 3” nailing blocks 
cut to fit the valley angle and curvature of the valley are 
spaced from 20” to 30” apart over the regular sheathing. 
Tapered strips 7%” x 2” or 3” wide are nailed over the 
blocks and lengthwise of the valley. 

The important consideration in any of these methods 


COMPOSITION TO WHICH SLATE CONCRETE 


ARE NAILED 


IWAIL/ING SCONCR ETE 


Geo CN ORAS 


is a solid foundation of accurate form to support the 
slates and establish the desired shape of the valley. 


Fireproof Construction 


For fireproof construction, a nailing concrete or gyp- 
sum slab are sometimes used, into which the slating 
nails are driven. The materials selected for this purpose 
should be given careful consideration as to their nail- 
holding power and durability. When a roof slab is not 
used, the slates are wired or otherwise secured to angle 
iron structural members. The slates are punched with 


four holes, wire run through each set of two holes and 
around the angle. The ends of the wire are then twisted 


(See Figure 40.) 


to fasten the slate tightly to the angle. 


Fireproof Construction to Receive Slate, Bennett Hall, 
University of Pennsylvania 


Special fasteners are sometimes employed to attach the 
slate to the angle. As the angles must be spaced the 
same as the exposure of the slates, long slates are to be 
preferred as they reduce the number of angles required. 


2) pe ye. 


CONSTRUCTION. 


Figure 40. Slate on Various Types of Fireproof Construction 


LOLA 


HE slope of a roof has been defined as the angle of 
| Ramen that the roof makes with a horizontal 
plane. The effect of this slope on the lap of the slate is 
shown in Figure 41. 

There are three methods of describing the slope of any 
First, in terms of vertical rise in inches to each 
Second, 
in terms of ratio of the total rise of the roof to its total 
span, as “14 pitch or slope”; that is, the height of the 
roof is equal to 14 of its total span. Third, in terms of 
degrees and minutes of the inclination of the roof to the 


roof. 
foot of horizontal run, as “1 inch to the foot.” 


horizontal plane. 

The slope is dependent upon climatic conditions and 
the design, and determines the method of laying the slate 
and the lap required. For further information, see 


page 15. 


in 


OVER 20 RISE TO / Foor 
STEEP ROOF 2° LAP 


ve 
8 
S) 
& 
els 
x 
Nie 
Ne 
6|? 
N 
ral 
4 
x 
aa é 
ye K 
Sy 8 
ae el 
<x 
Ny SIS 
Ko |. 
RAS aire 
NS 8 
YyIaSy x 
Q 
ca) 
So 
<2 
9 Xx « 
ue S| 
SESS 
KIN 
x 
<|8 
Ve RISE TO 1-0 RUN = F24 PITCH | L 


RUN OR 2 TOTAL SPAN 


Figure 41. Lap of Slate for Various Roof Slopes 


Eaves Troughs, Gutters and Conductor Pipes 


Upon the proper proportioning of the gutters and con- 
ductors or leaders will often depend the satisfactory 
performance of the roof. 

The size of leaders and gutters depends upon the 
amount of rainfall and the number of leaders used. One 
rule much in use is to provide 1 square inch of leader 


area for every 150 square feet of roof area. Leaders 


42 


should not be spaced more, and preferably less, than 75’ 
apart for flat roofs and 50’ apart for sloping roofs. 

All gutters should have a pitch of about 1” in 16’ in 
order that they may be washed clean during rainfall. 
Gutters made 2” larger than the leaders will permit a 
more practical connection than if made the same size. 

When more than 50’ apart, the leaders should be in- 
creased 1” for 


each additional 


20’ of space be- 

tween leaders for 

sloping roofs and Sy 

for each 30° for syesserS SSS 
fatereore ee SS 


A GUSSET IN GUTTER 
ANO SLOPING JO LEAD~ 
Hor more de- Ze: 


tailed information, 
refer to Part 3 of 
“Copper Flash- 
ings” handbook of 
the Copper and 
Brass Research 
Association, 25 
Broadway, New 
York City. 

Numerous kinds of gutters are in use, among them 
being the “hanging gutter,” which includes the “eaves 
trough” and the “moulded gutter”; the “box gutter,” also 
known as the “built-in” or “lined gutter”; several types 
of “standing gutters,” known by various names, and the 
“sunk gutter,” which is also sometimes called the “box” 
or “built-in gutter.” Each of these has its suitable use 
and location, as well as its disadvantages. 

The “eaves trough” is generally made in semi-circular 
section and hung from the eaves by metal hangers which 
are adjustable to regulate the gutter slope. “Moulded 
cutters’ are set true with the eaves line and are sometimes 


LMLARGED SECTION 
OF GUTTER SHOW- 
ING METHOD OF JOW- 
ING COPPER 


POLE GUTTER 


Figure 42 


9 


made with a sloped inner lining in order not to detract 
from the appearance of the building. 

There are many. types of hangers for “eaves troughs” 
or “hanging gutters.” It is advisable to select a type of 
hanger not fastened directly under the slate, as the weight 
of snow or ice collecting in the gutter may pry up to the 
hanger and break the slate. 

Hangers should be placed not further than 2’ 6” apart, 
because of the liability of the gutter sagging when insuf- 


NeAw igh OSNeAgT 


Seinen imis ease Gol ASbeL ON 


They should never be fastened 
rigidly to the gutter, as this will prevent the expansion 
and contraction of the metal. 

The “box gutter” is most suitable for a building having 
a wooden cornice. 
bottom of which is sloped. The metal lining should be 
carried over the eave mold and up the slope suflciently 


ficiently supported. 


It is in form a metal-lined box, the 


far to prevent damage if the gutter or outlet become 
clogged and water is not carried off promptly. 

One type of “standing gutter” is shown in Figure 42. 
In any type a cant strip should be placed under the 
lower courses of slate so as to form a drip at the edge 
and prevent water from being drawn up under the slate 
by capillary attraction and passing over the edge of the 
flashing. 

“Sunk gutters” are built below the surface of the roof 
and are lined with metal. They are closed at the ends 
so the crown mold can be run up to the gable. This type 


1 EAVES TROUGH 7 LEADER HEAD WEL. 
OR GUTTER: 8 LEADER OR 
2: GUTTERHANGER- CONDUCTOR. \t/ 


3: BASKET STRAINER 9° LEADER STRAP gh_-D=—(9) 


4 GUTTER OUTLET 10: SHOE: ae 

5 ELBOW: 1s NAILS. () & 

6 SCREEN: 12MITRE: (9) ( (6) 
13:CAP. eg) 


Figure 43. Parts of a Gutter 


of gutter, as well as the “standing gutter,” should always 
be placed as close as possible to the wall line of the house 
in order that the heat from the inside of the house may 
help melt any snow or ice which may form. The lining 
should be carried well up the slope. 

When gutters are placed behind parapet walls, the 
gutter and flashing should be formed of a continuous 
piece of metal, which should extend, if practicable, to 
the top of the coping and up under the slate to a point 
at least 3” above the top of the coping. If the gutter 
lining cannot be carried up to the top of the coping, it 
should be turned over and inserted in a reglet at a height 
of not less than 12”. It should be well wedged into the 
block with lead wool. The height to which the metal 
should be carried will be determined by the roof area 
drained, its slope, etc. On roofs of this character, it is 
essential that provision should be made for the escape of 
water if the leaders do not work. If the water is allowed 
to collect, it will not only cause a heavy and perhaps 
dangerous load, but may also work its way over the 


43 


flashings and down into the building. Scuppers large 
enough to preclude any possibility of clogging (at least 
4” by 12”) should be provided and should be unob- 
structed by screens or other devices. 

For inside leaders, a good grade of heavy cast iron 
or galvanized wrought iron pipe should be used and a 
trap provided when such leaders open near dormer win- 
dows or ventilating shafts. Outside leaders should be 
In climates where freezing 
occurs, a rectangular-shaped leader or one having corru- 


made of non-ferrous metal. 


gations is to be preferred to a smooth circular section, as 
the former provides 
room for expansion 
if ice forms in the 
leader pipe. 

Leaders are often 
made with ornamen- 
tal heads, and when 


COPPER STRAPS ABOUT 
JOINTHES APART RIVETED 
TO GUTTER AYD NAILED 
70 ROOF 


used, the goose necks 
offsets should 
empty into the head 
and not be joined to 
the downspout. If 
more than one fall 


or 


of gutter empties into MUNG GUTTE, 


the leader, a head 
should always be pro- 
vided. This should be of suitable dimensions to accom- 
modate the flow of water into it. 


Figure 44 


With any type of gutter it is essential that the water be 
led away as quickly as possible. This is especially im- 
portant in a climate where ice forms readily, as the snow 
will melt on the warm part of the roof, run on to the 
colder part and form ice in the gutter unless carried away 
at once. The ice will sometimes be heavy enough to 
bend or break the gutter and will almost always clog the 
downspout and back water over the edges of the gutter or 
on to the roof and under the roofing material. 

Provision should always be made against the choking 
of leaders or outlets by falling leaves or other débris, 
and strainers of wire or heavy metal, depending upon the 
flow of water and roof area, installed. Gutters and 
leaders should be inspected at least twice a year to remove 
leaves, rubbish, and repair or repaint if necessary. The 
fastenings of the gutter should be closely examined and 
strainers renewed when required. 


Leaders from higher or larger roofs should never be 
permitted to discharge water on to lower or smaller 
roofs, if such an arrangement can possibly be avoided. 
It is recommended that each gutter be individually 
drained down to the ground. Sometimes it is necessary 
to run the leader from a higher roof through the porch 


SUL VAT Ee ReORO ESS 


COPPER RIDIE PLASHINO 


ANOTHER METHOD OF 
SORMING RIDGE 


NAIL OR 


STANDING SIAM DPPER — 


FLAT SEALY COPPLR FEASHINE — 
LINE OF YIMNI/9L03 SHADOW \ 
AND BE SCCURED BY COPPER \ 
CLEATS SS SOLDERED LOCKED SEAM VERTICAL OR AT AH ANGLE 
SR TPMEOIN Tile CENTRE OF AL ACCORDING 7O DESIGN AND 
> SS GUTTERS OVER 18 IMHES MIDE LOCALITY 
ag NN 


FACE OF SAW TOOTH ROOF 


/ Saini SHADOW 
y= 
7——FLAT OR STANOING SEAM 
COPPER ROOPING = 
LOCKED SEW SOLDERED — 
va 4 

SOLDERED LOCKED ) 
SCAM FORMED IN THEGNTRE Ys 
OPAL GUTTERS OVER 12 fii 

WCHES WIDE—> 


AN INCORRECT METHOD OF LEGO) ANOTHER CORRECT METHOD OF [OR/1- 


GUTTLR SOR SAW TOOTH ROOF ING GUTTER [OR SAW TOOTH ROOF 


Figure 45 


roof to accomplish this, or carry the leader across the 
porch roof to the gutter. In the latter case the leader 
should never have a slope of less than 45°; otherwise, 
ice may form in the leader. When it does become abso- 
lutely necessary to discharge the water on to a lower roof, 
metal spreaders should be used. 

When a mansard roof is of slate and the deck is copper 
covered, it is sometimes advisable to frame a gutter in the 
deck because the drippings from the deck may discolor 
the slate. This gutter should be lined with cold rolled 
sheet copper and have a water outlet lead to the inside 
of the building. 

When a low roof drains into a leader from a high roof, 
it is sometimes advisable to install a trap in the lower 
roof leader. If this is not done, the water pouring down 
from the higher roof may back up on to the low roof. 

Adequate provision should always be made for carry- 
ing the water discharged by the leaders away from the 
walls of the building. This can sometimes be accom- 


2 


plished by “splash stones” or masonry gutters, or if the 
leaders do not connect with storm sewers, a cistern for 
rain water may be dug not closer than 50’ to the building. 
This may be lined to collect the water for household use 
or left unlined in order that the water may seep into the 
soil. The drain from leader to sewer or cistern should 


be placed below the frost line and slope about 1” in 10’. 


Simplified Sizes and Weights 


In accordance with the unanimous action on October 
14, 1924, of the general conference of representatives of 
manufacturers, distributors and users of eaves trough and 
conductor pipe, the United States Department of Com- 
merce, through the Bureau of Standards, recommends that 


simplified rules, practices, sizes and weights of eaves 
trough and conductor pipe be established as follows: 
Plain round conductor pipe: 2”, 3”, 4”, 5” and 0”. 
Round corrugated conductor pipe: 2”, 3”, 4”, 5” and 6”. 
Square corrugated conductor pipe: 2”, 3”, 4” and 5”, 
Eaves trough: 314”, 4”, 5’,67, 7” and 8”, 
Conductor pipe elbows: No. 1, 45°; No. 2, 60°; No. 3, 
vos No#4.90". 


1. Along with the elimination of certain sizes of con- 
ductor pipe and eaves trough goes also that of the fittings 
formerly used therewith. 

2. No eaves trough or conductor pipe to be made 
lighter than 28-gauge full weight; 27-gauge is to be elim- 
inated. 

3. All elbows, shoes, mitres and ali accessories, inclu- 
ding ridge rolls, valleys, gutters and so on, are to be of 
28-gauge full weight. 

4. All eaves trough, conductor pipe, shoes, mitres and 
all accessories, including gutters, valleys, ridge rolls and 
so on, when made of copper, to be not lighter than 16 
ounces. 

The 2” pipe should be used only for small roofs such 
as porches, etc., where there is a small amount of water 
to be carried away. 

The table below gives the nominal and actual sizes of 
the square corrugated pipe listed above: 


Nominal Size..... UE ou Altt 5" 
Actual Sizes 134" x 214 "1234" x 3M "1234" x 416 "1334" x 5" 


Snow Guards 

Snow guards are a necessary accessory to most slate 
roofs in sections of the country where the snowfall is 
sufficient to accumulate masses of snow and ice which are 


Figure 46. Snow Guards 


Ne ee ONE AG eer beer As eC. LAPT OUN 


liable to slide from the roof. On the slate roofs of the 
Harriman estate, along the Hudson, 35,000 copper wire 
snow guards were used. 

The appearance of many slate roofs in such localities 
has been marred by streaks of rust stains from such 
guards, or snow brakes, as they are sometimes called. 


FLASHING 
EAVES 


Figure 47. Parts of a Roof 


Years ago, according to one manufacturer, they mar- 
keted 90 black-painted guards to every 10 galvanized. 
But now, since research shows wisdom of proper installa- 
tions and better construction is demanded, this manufac- 
turer says he sells 75 galvanized to every 25 black- 
painted. 

While the “hot dip” process of galvanizing is the best, 
experts have still to be convinced that any galvanizing 
is perfect or rust proof. Hence, for first-class jobs only 
non-ferrous metals should be used for snow guards or 
any slate roof accessories. 

Snow guards should be placed in manner prescribed 
by their manufacturers on all slate roof surfaces above 


7 


SINGLE PITCH SHED ROOF 
OR LEAN 7O 


RIDGE 


DOUBLE ROOF OR GABLE ROOF 


HIP ROOF GAMBREL ROOF 


[ne HIP 


FRENCH OR MANSARD ROOF 


RiDck 
\ 
GAC 


GABLE ROOF WITH VALLEY 
AND H/P 


Figure 48. Types of Roofs 


doorways, porches, sidewalks, playgrounds or places 
where people are liable to pass or gather. They are 
essential to prevent masses of snow and ice from falling 
and as a protection to lower roof surfaces and gutters 
from such sliding masses. They are absolutely indis- 
pensable to retain snow on roofs when water from roof 
is collected for cistern or household purposes. 

Snow guards are made in various forms, some of which 
are illustrated in Figure 46. Each type requires different 
methods of application and may be obtained from slate 
distributors or quarriers of roofing slate or from manu- 
facturers. The Association can furnish a list of the latter 
concerns if desired. Some types may easily be placed on 
old roofs. 


Lightning Rods 

Where lightning rods are desired or used it is impor- 
tant at all times that they be properly grounded. All 
connections must be electrically perfect; that is, they 
must have very low contact resistance. Tips of rods 
should be silver, gold or platinum plated and all sharp 
bends in the conductor cable avoided. 

All extensive masses of metal such as water or gas 
pipe systems or cast iron soil pipe should be connected 
to the ground by soldered connections of not less than 
No. 10 B. & S. wire, preferably stranded. 

It is generally assumed that a lightning rod protects 
the area and any structures included within a 45° angle 
cone whose apex is the tip of the rod itself. 


Types of Roofs and Their Parts 


To the majority of the users of this Manual, the types 
of roofs and their parts will need no explanation but for 
the benefit of those not familiar with the names and 
technical descriptions used herein, reference to the accom- 
panying illustrations will provide the lay reader with the 
elementary information essential to a full understanding 
of the parts and types of roofs mentioned. 


Piling Slate 

In piling slate the important factors are the founda- 
lions, starting the piles, arrangement of piles and indi- 
vidual slates and the separations of the tiers. 


seal TE PILED HORIZONTALLY WITH HO THROUGH JOINTS 
/E NOT SUPPORTED BY | | I 
WALL AT THIS END VERTICAL SLATE | | 
OULD PILES OF SLATES i, | } 
FLIT ASAT OTHEREND Hl, 
\ Hill HI 
A® HORIZONTAL 
SLATE 
GROUND 


LATH OR STRAW 


SSS 
—— 
SS 


VERTICAL SLATE 


VERTICAL SLATE || 
ROPER MANE JOD SOR PLING OLA TE. 


Figure 49 


Silene sie he OrOeisS 


The earth foundation upon which the slate are to be 
piled should be level, dry and solid. A layer of two-inch 
plank will keep the slate off the ground, help to dis- 
tribute the load and assist in maintaining straight even 
piles. The tiers of slate cannot be kept level if the 
foundation is not even or free from settlement. 

The first tier should be started by laying one pile of 
slates flat to a height equaling the width of slate being 
piled; i.e., for 20” x 12” slate the flat pile is 12” high. 

The following slates of the first tier are placed in an 
upright position on edge lengthwise, and should be kept 
as straight and vertical as possible. The bottoms of 
each handful should be tight against the bottom of the 
preceding slates. In this way the top is maintained 
straight and level. 

After the first tier has been laid to the desired or a 
convenient length, lay a double row of wooden lath 
lengthwise over the top of the first tier. Place the lath 
1” from the outside edges of the slate tiers and interlap 
each lath one or two inches. A liberal quantity of straw 
may be used as a substitute for the lath. 

Rest the flat or starter of the second tier one half on 
the first tier starter and one half on the upright slates. 
This will help to prevent the piles from overturning and 
“slumping” down obliquely. Keeping the following 
slates as nearly perpendicular as possible is especially 
important in the first two tiers. 

Slates up to and including 20” x 11” may be safely 
piled up to 6 tiers high. Slates of a larger size should 
never be piled more than 4 tiers high. Closely piled, 
100 commercial standard slates average 20” to 24”. 

When the slates are stored in an open yard, cover the 
piles with overlapping boards or use tar paper weighted 
down. Adequate protection prevents the slates from 
being frozen together. While slates are of ample strength 
when used in their proper place, reasonable care should 
be used in the handling of the material. 


Estimating Slate Quantities and Costs 


Architects and others interested should confer with 
local roofing contractors and through them obtain the 
“per square” or approximate total price for a particular 
type of roof, or have them estimate the quantities re- 
quired and furnish a definite price for each individual 
roof. Producers are always glad to co-operate with roof- 
ing contractors to furnish architects a layout or recom- 
mendations for slate suitable for any design or desired 
effect and to furnish roofing contractors estimates so they 
can give architects or owners comparative cost data to 
assist them to arrive at amount to spend for slate roof. 

A mistake frequently made is that of measuring the 
roof surface and assuming it as the exact or very close 


46 


approximate quantity required, then multiplying it by a 
price quoted in the price-list of one of the slate com- 
panies and perhaps adding an assumed sum for labor 
and contractors’ profit. 

In preparing estimates for a slate roof, every roofing 
contractor has his own method of making compensating 
allowances for waste, breakage, projections through 
roofs, dormers, hips, ridges, valleys and other factors 
occasionally entering into the question of quantity and 
labor. These are usually based upon experience with 
his own regular labor, local conditions or practice, and 
possibly other items peculiar to a locality. The follow- 
ing suggestions are therefore offered mainly for archi- 
tects and others not actively engaged in selling and lay- 
ing slate roofs, as a guide to many factors which should 
to be taken into consideration. For rough estimates a 
good roof costs from 6 to 8 per cent of total cost average 
building or home. 

From the time work is first started at the quarry until 
the material is laid on the building, there are certain costs 
which must be taken into consideration. These may be 
listed as follows: 


1. Cost of slate (punched) on cars at the quarry. 

. Freight from quarry to destination. 

. Loading and hauling to storage yard. 

. Unloading, piling and waste at storage yard. 

. Loading and hauling to job. 

. Unloading and piling at job. 

. Placing on roof and laying. 
(a) Roofing felt. (b) Elastic Cement. (c) Nails. 
(d) Snow guards, or Snow Rails. (e) Sheet Metal. 
(f) Labor, including compensation insurance.. 
(g) Waste in handling, cutting and fitting. 

8. Contractor’s overhead on organization and equip- 


NAN S& w bv 


ment. 
9. Cost of guarantee or Bond. 
10. Contractor’s profit. 


Items 3 and 4 are omitted when material is hauled 
direct to the job and unloaded. Freight to any locality 
from a quarry remains a fixed charge based upon either 
carload or less than carload lots. Less than carload lots 
carry a freight charge about double that of carload quan- 
tities. The question of loading, hauling, unloading and 
laying depends upon local labor costs, how fast the men 
work and nature of the contractor’s equipment. Some 
roofing contractors have slate punching machines and buy 
their slate unpunched, punching same at the job or in the 
yard on idle days or during inclement weather. 

While it may seem a comparatively simple problem to 
estimate the net quantity, it is not so easy to allow for 
the additional material required for slate around chim- 


neys, dormers, hips, valleys, etc. These allowances de- 


Ne Ace LL OUNe Ad 


Silane hae ao OG WAST IT OEN 


pend largely upon the judgment and experience of the 
estimator and the roof design. 


Method Suggested for Estimating 

1. Obtain the net area of the roof in square feet, adding 
6” to rafter length to allow for waste of normal roof. 

2. Deduct one-half of the area of chimneys and dormers 
if over 20 sq. ft. and less than 80 sq. ft. Make no 
deduction if less than 20 sq. ft., and deduct 20 sq. ft. 
less than actual area if more than 80 sq. ft. 

. Include areas of dormer roofs, sides of dormers if 
slated, slate saddles, or other places where slate is 
used in addition to the main roof area. Include over- 
hanging parts of dormers, etc. 

4. Add 1 sq. ft. for each lineal foot of hips and valleys, 

for loss in cutting and fitting. 

5. Allow from 2% to 15% additional slate, depending 
upon the extent to which the roof is intersected by 
other roofs, dormers, walls, other contingencies, etc. 

6. Divide the total of the above by 100, which will give 
the number of “squares” of roofing required. 

It should be noted that slate is always sold at the 
quarry on the basis of the quantity required to cover 
“100 sq. ft.” or a “square” of roof when slate is laid 
with a 3” head lap. If the roof is flat or other than 3” 
lap is used, the quantity must be corrected to the equiva- 
lent amount required as though the 3” lap was used. 
The following information should be given local roofing 
contractor when asking for a price: 


co 


1. Kind and color of slate. 

2. Size of slate desired, stating length and “all one 
width” or random width. 

3. Thickness, as “commercial standard,” 14”, 3%”, etc. 

4. Type of roof, as standard, textural, graduated or flat. 

5. Kind of nails, as zine clad, zinc, “yellow metal,” 
copper clad or copper. 


6. Kind of valleys and flashings. 

7. If hip or gable roof. 

8. Kind of snow guards, as galvanized, yellow metal or 
copper. 

9. If snow rails, size of pipe and number of rows of 
pipe. 

10. Location of job; if in city or vicinity, or out of city. 

11. When job is to be finished. 

Prices 


Many requests have been received from architects and 
builders for the inclusion in this book of a definite list 
of prices for the various grades and colors of roofing 
slates. The compilers regret that it is impracticable to 
do this, for several reasons. The Association recom- 
mends, therefore, that when an architect or builder de- 


47 


sires the price of any particular grade and color of slate, 
he consult his local slate roofing contractor for estimates 
for the slate in place on the roof. Such estimates will 
then include the many factors listed in the section on 
“Estimating,” all of which must be given consideration. 
This can best be given by responsible contractors who 
are familiar with local conditions and costs. 


Advantages of Slate 

During the preparation of this book many requests 
to include in it a list of the advantages of slate in direct 
comparison with other roofing materials were received 
from architects, contractors, and especially from pros- 
pective home builders. 

The policy of the National Slate Association is, and 
always has been, never to point out the faults or weak- 
nesses of a competitive or a substitute material for any 
of the uses of slate. Such procedure conforms with 
sound business ethics, and, in line with this policy, the 
editors merely list in convenient form the outstanding 
characteristics which make slate such a valuable roofing 
material. Each of these qualities will be found discussed 
elsewhere in this book. 


Natural Stone 
Non-combustible—F ireproof 
Waterproof 
Permanent 
Wide range of effects possible 

Appearance 

Color 

Thickness 

Surface Texture 

Roof Texture 
Little or no maintenance costs 
Resists climatic changes 
Requires no other material to preserve it 
Reduces insurance premiums 
High salvage value 
Increases property values 


Investigation has shown that the cost of the roof of 
any structure ought to bear a certain definite relation to 
the cost of the entire building, not only from the stand- 
point of protection, but also from appearance. Every 
permanent building should be roofed with a material 
which will give it lasting protection, and at the same time 
be in character with the house itself and its surroundings. 
Because it does possess these qualities, for centuries slate 
has been the criterion by which other roof coverings have 
been judged. A slate roof has that indefinable “some- 
thing” which distinguishes any object of real value and 
completes the picture of a well constructed building or 
home. 


as 
SPECIFICATIONS, | 


GENERAL NOTES—ALL SPECIFICATIONS 


(a) The following specifications for “Standard,” “Textural” and “Graduated” slate roofs give in detail the pro- 
cedure to be followed in the laying of each type of roof on any type of structure from the smallest bungalow to the 
largest mansion. 

(b) A “Short Form” of each of these specifications is given just ahead of the “Basic Form” and is intended to 
be written into the architect’s specification. The “Short Form” refers to the “Basic Form” of the National Slate 
Association as printed herein and carries with it all the provisions contained in the “Basic Form.” In each “Short 
Form” the architect should fill in the color and size of the slate desired; otherwise it is complete as printed. 

(c) It will be noted that the “Sheet Metal Work” is a separate specification. The architect or owner can use it 
as a separate specification if this work is the subject of a separate contract or add it to the slate roofing specification 
if it is to be part of the slate roofing contractor’s work as is the custom in certain localities. 

(d) In each specification it is assumed that sheathing boards, crickets, cant strips or other under-roof surface 
will be specified elsewhere under the proper trade. 

(e) The marginal notes are informative and indicate optional changes which may be made in the specifications. 

(f) These specifications do not in any case include General Conditions or items relative to administrative mat- 
ters such as usually form the first part of an architect’s specification. Such items include fire, compensation, liability 
or other insurance and the use of hoists, water, telephone, watchman, temporary heat and light, and storage. 

(¢) The attention of the architect and owner is called to this fact in order that they may be fully acquainted 
with all conditions and advise the roofing and sheet metal contractor to arrange for the proper disposition of such 
items with the owner when the contract is direct or with the general contractor when his status is that of a sub-con- 
tractor. 

(h) The National Slate Association recommends the use of the Standard Documents of the American Institute of 
Architects and especially the “Standard Form of Sub-contract” which is a form of agreement between the General 
Contractor and the Sub-contractor. It calls attention, however, to paragraphs f and g above as these subjects are only 
covered in a general way in the “Standard Form.” 


STANDARD SPECIFICATIONS 


FOR 
SHEET METAL WORK 
IN CONNECTION WITH A SLATE ROOF 


NOTES 


1. This specification used as here given will provide for sheet metal work in connection with a slate roof as 
follows: 
Paper—Rosin sized or asbestos felt, 6 lbs per sq. (unless already covered for slate) 
Nails—Copper. Flashings—16 oz. copper. 
Valleys—Open. 


2. The following must be written into the specification, if required: 
Decks, Cornices, ete. 
Gutters and Downspouts. 


3. See also General Notes—All Specifications, page 48. 
48 


ING Agel OpeNg Agee oe oe ep sek eh A On oe Orl As ly OUN 


SHORT FORM SPECIFICATION 
1. Sheet Metal Work 


All materials and labor in connection with all sheet metal work shall be furnished and performed in strict com- 
pliance with the recommended practice and Standard Specification “M” for Sheet Metal Work, 1925, of the National 
Slate Association, 791 Drexel Building, Philadelphia, Penna. 


2. Decks, Cornices, Etc. If required specijy materials and methods. 
3. Gutters and Conductor Pipes If required specify materials and methods. 


STANDARD SPECIFICATION “M” 


(Covering in detail Flashings, etc., in connection with a Slate Roof) 
1. General and Guarantee . 


(a) The General conditions of the contract are hereby made a 
part of the contract and this contractor shall examine these General 
Conditions and thoroughly acquaint himself with all the require- 
ments therein contained. 

(b) This contractor shall furnish all materials and labor in ac- 
cordance with the drawings and these specifications. 

(c) This contractor shall carefully examine all surfaces prepared 
for flashings, etc., by other trades, shall point out all defects to the 
proper authority, and shall see that the necessary corrections are 
made before proceeding with his work. 

This contractor shall arrange his work so as to co-operate at all 
times with other trades and prevent delay or damage to other work. 

(d) During construction care shall be taken to prevent damage 
to flashings in place by walking or placing heavy materials on them. 
As soon as soldering is done and flashings are completed, the work 
shall be thoroughly cleaned. Toward completion, all damaged 
work shall be repaired, all stains and débris shall be removed, and 
sheet metal work shall be left in perfect condition. 

(e) The contractor shall furnish his own scaffold or rigging, or 
arrange with the general contractor for the use of scaffolds furnished 
by others. 

(f) A written guarantee shall be furnished that the materials used 
are in strict accordance with these specifications, and that any and 
all repairs required on the roof due to defective materials or work- 
manship furnished under this contract shall be made without cost to 
the owner, for a period of one year. 


2. Preparation of Surfaces 


All surfaces to receive flashings shall be made smooth and even, 
and all nail heads shall be set. 


3. Building Paper 

All surfaces to be covered with copper shall be covered first with 
rosin-sized or asbestos-felt paper weighing not less than 6 pounds 
per 100 square feet. Paper shall lap 2” and be nailed with flat-head 
copper nails. If surfaces have already been covered with paper or 
felt by the roofing contractor this paper may be omitted. 


4. Nails and Fastenings 


All nails, rivets and similar fastenings, if any, used throughout the 
work shall be of best grade hard copper or brass. Nails shall be 
wire nails not less than No. 12 gauge and not less than 7%” long. 


5. Copper 
All flashings shall be 16 ounce soft copper, rolled from copper If other than copper is to be used, specify materiat, 
conforming to the standard specification of the American Society for gauge, weight, painting and method of laying. 


Testing Materials. The edges of all sheets to be soldered shall be 
tinned 114” on both sides. 


49 


SULBARL FER nO sOghaS 


eee 


6. Solder and Rosin 


All solder shall be of the best grade, equal to Specification 
B-32-21 of the American Society for Testing Materials, and shall 
be composed of one-half pig lead and one-half block tin (new 
metals). Rosin shall be used as a flux. 


7. Exposed Edges 


The exposed edge of all flashings shall be folded under 14”, in 
in such manner as to conceal them from view. 


8. Flashings—Where Required 


All intersections of roofs with vertical surfaces of every kind and 
all openings in roof surfaces, shall be flashed with copper. The 
method of flashing, except as otherwise shown or specified, shall 
be base and counter, or cap, flashing. 


9. Base Flashings 


(a) Unless otherwise specified or shown on the drawings, base 
flashings shall be, in general, at least 4” high. They shall project 
at least 4” out on to the roof. Flashings shall be full 96” in length. 
On sloping roofs they shall lap longitudinally at least 3”. On flat 
roofs the joints shall be flat-locked and soldered. 

(b) Against stucco-coated walls, metal lath shall lap outside the 
flashing so that the stucco shall finish over the flashing. 


10. Cap Flashings or Counterflashings 


Cap flashings shall turn down over base flashings not less than 4”. 
They shall be secured to vertical surfaces, as follows: 

Wood Work: They shall extend up under exterior coverings not 
less than 4” above the roof, and shall be nailed along the top edge 
about every 8”. 

Mason Work: They shall extend into joints of masonry walls 4” 
and have the inner edge turned back on itself 14”. The sheets shall 
be bent to the required shapes, and built in with the mason work. 
No cutting out of joints for setting flashings will be allowed. 

Reglets: Where indicated on the drawings or where specified, 
flashings shall finish in reglets in the masonry cut by others where 
located by this contractor. 

The flashing shall be turned into the reglet the full depth and 
shall be turned back to form a hook. 

After the flashing is in place the reglet shall be filled and caulked, 
using molten lead on flat surfaces, and lead wool on vertical surfaces. 

After caulking the reglet shall be made smooth by filling with 
elastic cement. 

Stucco on Wood: When used with stucco-covered wood-frame 
walls, cap flashings shall be formed over a 7%” base board and 
extend up the wall at least 2” above the base board, and be nailed 
at the top edge with nails about 12” apart. Metal lath shall be 
placed over the flashing and the stucco should be finished against 
the base board. 

Stucco on Masonry: They shall be built into the masonry as the 
work progresses and shall project out from the wall as required and 
turn down over the base flashing. The stucco shall finish against 
the cap flashing. 

Concrete Walls: They shall be set in the forms before the con- 
crete is poured. They shall extend into the wall at least 2” and 
shall have the inner edges turned back 14”. 


50 


Specification writer should include here only those 
paragraphs which apply to the work and make suit- 
able provision in mason and carpenter specification 
for preliminary work. 


Make provision in proper specification for base- 
board, metal lath, etc. 


Ng oe ee OnE Ag 


Sele be eer. LOA alZOnN 


11. Step Flashings 


Step flashings shall be used where vertical surfaces occur in con- 
nection with slopes. They shall be formed of separate pieces built 
into the masonry as specified for cap flashings in masonry. Steps 
shall lap generally 3”, but in no case less than 2”, and shall not 
be soldered. Lap joints shall be vertical. 


12. Vent Flashings 


All pipes passing through roofs shall be flashed and counter- 
flashed. Base flashings shall extend out on the roof not less than 6”. 
They shall be of sufficient length to cover the slate course next below 
the pipe and to extend up under the slate course above as far as 
possible without puncture by nails. 

Patented vent-flashing devices may be used, subject to the approval 
of the architect. They shall be made of 16 ounce copper, shall be 
the product of a recognized manufacturer, and shall be installed 
according to manufacturer’s directions. 


13. Open Valley Flashings 


(a) Open valleys shall be not less than 4” wide. The proper 
width shall be determined by the following rule: 

Starting at the top with a width of 4”, increase the width one 
inch for every 8 feet of length of the valley. Flashing pieces shall 
be full length sheets and of sufficient width to cover the open por- 
tion of the valley and extend up under the slate not less than 4” 
on each side. 


(b) Where two valleys of unequal size come together, or where 
the areas drained by the valley are unequal, there shall be placed 
in the valley a “crimp” angle or tee not less than 1” high. This 
“crimp” may be formed in the valley sheet before placing, or it may 
be made of a separate piece soldered to the valley sheet. 


14. Crickets or Saddle Flashing 

Crickets or saddles formed back of all vertical surfaces, such as 
chimneys, etc., breaking through sloping roofs, shall be covered with 
copper. The flashing of these crickets shall be made of part of the 
flashing along the sides of the chimney, etc. 


15. Other Work 


This contractor shall furnish all flashing pieces to other trades 
such as the Mason, Carpenter and Roofing Contractor for building 
in with that particular work and shall co-operate with these con- 
tractors in doing their work. 


16. Decks, Cornices, Ete. 


17. Gutters and Down Spouts 


If closed valleys are desired, specify as follows: 

Flashing pieces, for closed valley shall be of suj- 
ficient length to extend 2 inches above the top of slate 
roofing piece and lap the flashing piece below 3 
inches, and of width sufficient to extend up the sides 
of the valley far enough to make the valley 8 inches 
deep. 


They shall be placed with the slate so that all 
pieces are separated by a course of slate. Pieces shall 
be set so as to lap at least 3 inches and to be entirely 
concealed by the slates. They shall be fastened by 
nails at the top edge only. 


A small inequality in the areas drained would not 
require this. 


Specify framing and blocking for crickets under 
carpentry. 


Make provision in mason specifications for building 
in these flashings, and the cutting of any necessary 
reglets. 


If required specify materials and methods. 


If required specify materials and methods. 


Standard Specification “M”—Sheet Metal Work, 1925 


ol 


ed bate) BS yea O(a bd Beas 


STANDARD SLATE ROOFS 


The “Standard” slate roof has been developed to provide a serviceable, permanent roof at a minimum cost. 
Any changes which have been made in the usual specification do not in any way affect those valuable features which 
are to be found only in a slate roof but merely eliminate so far as possible every factor which might increase the 
cost of slating. 

As has previously been explained, the nature of slate stone is such that every piece cannot be split to an exact 
thickness and in order to eliminate a selection of the material with its resultant rehandling and calipering of each 
piece, a slight variation in the thickness of the slates is permitted. “Commercial Standard” slates are the quarry 
run of production and may show tolerable variations above or below 3/16”. 

A second change is found in the note opposite paragraph 3, page 53, of the Specification. The Architect or 
Owner will find it to his advantage to confer with the roofing contractors in his locality regarding the size (length 
and width) or sizes of the slate economically available. The number of sizes shown on page 12 is due to the 
nature of the material which makes it necessary to cut the blocks into a large number of different sized pieces 
to secure the fullest utilization of the slabs as they are taken from the quarry. 

It will therefore be readily appreciated that certain sizes may be more easily obtained than others and that to 
insist on slates of a definite dimension may not only add to the cost of the roof but may delay the work owing 
to difficulty in locating a quarry having that particular size in stock. On roofs of large area sufficient economy can 
often be effected by a proper selection of sizes to make a preliminary investigation of value. The smaller sizes 
ranging from 10” x 6” to 14” x 10” are usually more plentiful than the larger sizes and when laid with a narrow 
exposure will be found to produce a most interesting and artistic effect similar to that secured in the same way on the 
wonderful chateaux of France. 


STANDARD SPECIFICATION 


FOR A 
STANDARD SLATE ROOF 
NOTES 
1. This specification used as here given will provide for a complete slate roof as follows: 

Felt—Saturated Asphalt, 14 lbs. per sq. Ridges—Saddle 

Flashings—16 oz. copper Nails—Copper 

Valleys—Open Slate—Commercial 
Hips—Saddle standard (approx. 3/16”) 


Cement—Elastic waterproof 
2. The following must be written into the specification under paragraph: 


3-b. Slate—size 
3-c. Slate—color 


3. It should be noted that metal work is not covered by this specification, as separate Standard Specifications for 
Sheet Metal Work are given on page 48. The specifications for Slate Roofing and sheet metal work are so arranged, 
however, that they may be handled separately or together to conform to variation in custom in different sections of 
the country. 

4. See also General Notes—AlIl Specifications, Page 48. 


SHORT FORM SPECIFICATION 
Note: In using the Short Form if any optional paragraphs are desired so state. 


1. Slate Roofing For standards and optional materials and methods, 


; : : : see the following paragraphs in the complete form. 
(a) Furnish all materials and labor and cover with commercial = oe 


s rt f the building sh arked or indi- Paragraph 1—Guarantee 
standard slate all portions of the building shown, marked or indi Pe ee ein 


cated for Slate, and form all slate hips and ridges in accordance Patasraphs = Slave 
with Specification S for a Standard Slate Roof, 1925, of the National Paragraph 4—Hips 
Slate Association, 791 Drexel Building, Philadelphia, Pa. Paragraph 5—Ridges 


Paragraph 6—V alleys 

Paragraph 7—Elastic Cement 

Paragraph 8—Nails 
(Continued on Page 53) Paragraph 9—Slating 


a2 


Nee ele ORN Ag 


Sole ie te ARS nO CU lAsL LO aN 


(b) The size of the slate shall be 
(c) The color of the slate shall be 


2. Sheet Metal Work 


Paragraph 3-b—Size of Slate 
Paragraph 3-c—Color of Slate 


If part of the slate roofing contractor's work, quote 
here the Short Form for Sheet Metal Work on 
page 49. 


STANDARD SPECIFICATION ‘S” 


(Covering in detail all materials and labor in connection with a Standard Slate Roof) 


1. General and Guarantee 


(a) The General Conditions of the contract are hereby made a 
part of the contract and this contractor shall examine these General 
Conditions and thoroughly acquaint himself with all the require- 
ments therein contained. 

(b) This contractor shall furnish all materials and labor in ac- 
cordance with the drawings and these specifications. 

(c) This contractor shall inspect all surfaces prepared for slating 
by other trades, point out to the proper authority all defects, and 
shall not proceed with the laying of felt, flashings or slate until the 
necessary corrections have been made. 

(d) Roofing shall be applied by workmen experienced in the 
applying of slate. 

(e) The roofing contractor shall furnish his own scaffold or rig- 
ging, or arrange with the general contractor for the use of scaffolds 
furnished by others. 

(f) A written guarantee shall be furnished that the eat 
used are in strict accordance with these specifications, and that any 
and all repairs required on the roof due to defective materials or 
workmanship furnished under this contract shall be made without 
cost to the owner, for a period of one year. 


2. Roofing Felt 


(a) On all boarding to be covered with slate, furnish and lay 
asphalt saturated rag felt, not less in weight than that commercially 
known as “14 pound” felt. In this weight, per 100 square feet, a 
tolerance of one pound plus or minus will be allowed. 

(b) Felt shall be laid in horizontal layers with joints lapped 
toward eaves and at ends at least 2” and well secured along laps and 
at ends as necessary to properly hold the felt in place and protect 
the structure until covered by the slate. All felt shall be preserved 
unbroken, tight and whole. 

(c) The felt shall lap over all hips and ridges. 

(d) Felt shall be lapped 2” over the metal of any valleys or 
built-in gutters. 


3. Slate 
(a) Slate shall be of commercial standard quality and thickness. 


(b) Size of slate shall be 
of length(s). 


, or random widths 


(c) Color of slate shall be 


(Continued on Page 54) 


53 


For additional data regarding roofing felt, see 
page 23. 


Commercial standard slate is approximately 3/16” 
in thickness. If any other thickness is desired, so 
state and omit “Commercial.” 


For table of standard sizes, see page 12. 

A definite size must be stated to place all estimates 
on an equal basis. 

To obtain a roof at a minimum cost, confer with 
local roofers as to the size or sizes economically 
available. Standard roofs are usually laid with slate 
of one size on any one area. If random widths are 
desired, so state. 


For list of slate colors see page 7. 

Ij weathering slate are desired, so state, otherwise 
unfading colors will be furnished. 

If @ particular quarry product is desired, so state. 


Se beg Ee SReOeOsikes 


(d) All slate shall be hard, dense, sound rock, machine punched 
for two nails each. All exposed corners shall be practically full. 
No broken corners on covered ends which sacrifice nailing strength 
or the laying of a watertight roof will be allowed. No broken or 
cracked slates shall be used. 


4. Hips 


(a) All hips shall be laid to form “Saddle” Hips without metal 
underneath. 


5. Ridges 


(a) All ridges shall be laid to form “Saddle” Ridges. The nails 
of the combing slate shall pass through the joints of the slates below. 


6. Valleys 
(a) All valleys shall be laid to form “Open” Valleys. 


7. Elastic Cement 


(a) Cement shall be an approved brand of waterproof elastic 
slaters’ cement colored to match as nearly as possible the general 
color of the slate. 


8. Nails 


(a) All slate shall be fastened with two large-head slaters’ solid 
copper nails. Use 3d (114”) nails for slates 18” or less in length, 
4d (144") for 20” or longer, and 6d (2”) for slates on hips and 
ridges. 


9. Slating 

(a) The entire surface of all main and porch roofs, the roofs and 
sides of any dormer windows, if shown, and all other surfaces so 
indicated on the drawings, shall be covered with slate in a proper 
and watertight manner. 

(b) The slate shall project 2” at the eaves and 1” at all gable 
ends, and shall be laid in horizontal courses with the standard 3” 
headlap, and each course shall break joints with the preceding one. 
Slates at the eaves or cornice line shall be doubled and canted 14,” 
by a wooden cant strip. 

(c) Slates overlapping sheet metal work shall have the nails so 
placed as to avoid puncturing the sheet metal. Exposed nails shall 
be permissible only in top courses where unavoidable. 

(d) Neatly fit slate around any pipes, ventilators, etc. 

(e) Nails shall not be driven in so far as to produce a strain on 
the slate. 

(f) Cover all exposed nail heads with elastic cement. Hip slates 
and ridge slates shall be laid in elastic cement spread thickly over 
unexposed surface of under courses of slate, nailed securely in place 
and pointed with elastic cement. 

(¢) Build in and place all flashing pieces furnished by the sheet 
metal contractor and co-operate with him in doing the work of 
flashing. 

(h) On completion all slate must be sound, whole and clean, and 
the roof shall be left in every respect tight and a neat example of 
workmanship. 


“Machine punched” does not exclude hand punch- 
ing by means of the punch and mawl or hand punch- 
ing with the hammer, as the slate is laid, to properly 
locate holes for fitting hips, etc., or obtaining suitable 
nailing to the roof boards. 


Ij any other type of hip is desired, so state. 


Ij combed ridges, ridge rolls or cresting are desired, 
so state. 


If “Closed” Valleys are desired, so state. 


Vertical surfaces may be laid with 1” headlap. 

Specify cant strips of proper thickness under 
Carpentry. 

Where cant strips occur above gutters, they should 
be placed before the metal. 


Standard Specification “‘S’”—Standard Slate Roof, 1925 


National Slate Association 


o4 


Neel Om Ne Ag ogee eta encore On. AN TOL OFN 


TEXTURAL SLATE ROOFS 


The term “Textural” is applied to slate roofs in this publication for the first time, so far as is known. It has been 
here coined to designate those charming roofs of slate which cannot be classified as strictly Standard or Graduated 
but which range between the two and produce a distinctive and altogether individual result. 

The Textural roof presents most fascinating possibilities to the designer, for it may be varied in almost hundreds 
of ways to conform and harmonize with the structure of which it is to become a part. It may be made nearly as 
chaste as the Standard or it may be almost as elaborate as the Graduated. For example, the slates may be uniform in 
length but vary in thickness, or the thickness may be kept uniform and the length (and exposure) varied. The width 
may vary or be uniform. Very rough surfaced slates may be introduced into an otherwise almost smooth roof. The 
slate may be laid with varying exposure or the butts may be chipped and broken at irregular angles. When the thick- 
ness is varied the usual range is from 3/16” to 3%” but if a heavier and more irregular effect is desired, this may be 
accomplished by incorporating certain percentages of thicker slates. 

These present only a few of the opportunities for interesting treatment. In addition, the color of the slates may be 
used with splendid effect by mixing slates of different tones, but the tone value or predominating color effect desired 
should always be specified. When color is used, accidental or “freak” slates may be introduced throughout the roof, 
adding greatly to the picturesque effect of the ensemble. 

The cost of a Textural roof will depend entirely upon the effects desired, and although usually slightly greater 
than the Standard roof, will not equal in either material or labor the cost of a Graduated roof. 

The various details of construction, sheathing, ridges, hips, valleys, flashings, etc., shown in connection with the 
Standard slate roof apply also to the Textural roof. The construction may require additional collar beams, supports 
or slightly heavier rafters than for a Standard roof, depending upon local conditions and construction as well as the 


weight of the slate selected. 
STANDARD SPECIFICATIONS 


FOR A 
TEXTURAL SLATE ROOF 
NOTES 


1. This specification used as here given will provide for a complete slate roof as follows: 


Felt—Saturated Asphalt commercially known as 30 lbs. per sq. 


Flashings—16 oz. copper. Slate—3/16” to 34”, random width, approved lengths. 
Valleys—Closed. Hips—Saddle. 
Cement—Elastic Waterproof. Ridges—-Saddle. 


Nails—Copper. 
2. The following must be written into the specification under paragraph: 
3-c Slate—Predominating color. 

3. It should be noted that metal work is not covered by this specification, as separate Standard Specifications for 
Sheet Metal Work are given on page 48. The specifications for Slate Roofing and sheet metal work are so arranged, 
however, that they may be handled separately or together to conform to variation in custom in different sections of 
the country. 

4. See also General Notes—All Specifications, Page 48. 


SHORT FORM SPECIFICATION 


Note: In using the Short Form if any optional paragraphs are desired so state. 


]. Slate Roofing For standards and optional materials and methods. 
(a) Furnish all materials and labor and cover with slate all por- See the following parcgraphs.th the complete jor: 
tions of the building shown, marked or indicated for slate, and Sep pause 
form all slate hips and ridges in accordance with the Specification ye Del adlad le tel 
ees 5 2 Paragraph 3—Slate 
T” for a Textural Slate Roof, 1925, of the National Slate Asso- Paragraph 4—Hips 
ciation, 791 Drexel Building, Philadelphia, Pa. Paragraph 5—Ridges 


Paragraph 6—Valleys 

Paragraph 7—Elastic Cement 

Paragraph 8—Nails 
(Continued on Page 56) Paragraph 9—Slating 


Sys) 


Sale he ROL OsKesS 


(b) The predominating color of the slate shall be 
2. Sheet Metal Work 


Paragraph 3-b—Sizes of Slate 
Paragraph 3-c—Color of Slate 


If part of the slate roofing contractor’s work, quote 
here the Short Form for Sheet Metal Work on 
page 49. 


STANDARD SPECIFICATION “T” 


(Covering in detail all materials and labor in connection with a Textural Slate Roof.) 


1. General and Guarantee 


(a) The General Conditions of the contract are hereby made a 
part of the contract and this contractor shall examine these General 
Conditions and thoroughly acquaint himself with all the require- 
ments therein contained. 

(b) This contractor shall furnish all material and labor in 
accordance with the drawings and these specifications. 

(c) The roofing contractor shall furnish samples of the slate he 
proposes to use. If required, a layout shall be prepared by the 
producer and submitted to the Architect for approval. 

(d) This contractor shall inspect all surfaces prepared for slating 
by other trades, point out to the proper authority all defects, and 
shall not proceed with the laying of felt, flashings or slate until the 
necessary corrections have been made. 

(e) Roofing shall be applied by workmen experienced in the 
applying of slate. 

(f) The roofing contractor shall furnish his own scaffold or rig- 
ging, or arrange with the general contractor for the use of scaffolds 
furnished by others) 

(g) A written guarantee shall be furnished that the materials 
used are in strict accordance with these specifications and the samples 
submitted, and that any and all repairs required on the roof due to 
defective materials or workmanship furnished under this contract 
shall be made without cost to the owner, for a period of one year. 


2. Roofing Felt 


(a) On all boarding to be covered with slate, furnish and lay 
asphalt saturated rag felt, not less in weight than that commercially 
known as “30 pound” felt. 

(b) Felt shall be laid in horizontal layers with joints lapped 
toward eaves and at ends at least 2” and well secured along laps and 
at ends as necessary to properly hold the felt in place and protect 
the structure until covered by the slate. All felt shall be preserved 
unbroken, tight and whole. 

(c) The felt shall lap over all hips and ridges. 

(d) Felt shall be lapped 2” over the metal of any valleys or 
built-in gutters. 


3. Slate 
(a) Slate shall be in combinations of thicknesses from 84” to 


3/16” thick. 
(b) Slates shall be of random widths and of such lengths as 
approved by the Architect. 


(c) The predominating color of the slates shall be 


(d) All slate shall be hard, dense, sound rock, machine punched 
for two nails each. No cracked slate shall be used. All exposed 
corners shall be practically full. No broken corners on covered 
ends which sacrifice nailing strength or the laying of a watertight 
roof will be allowed. No broken or cracked slates shall be used. 


36 


For additional data regarding roofing felt, see 
page 23. 


If a percentage of thicker slates are desired, state 
the thickness and percentage of each. 


If a layout is required, state—‘in accordance with 
approved layout.” If definite sizes must be furnished, 
so state. To obtain a roof at minimum cost, confer 
with local roofers as to sizes economically available. 


For list of slate colors see page 7. 
Colors will be of the “weathering” class unless 
otherwise noted. 


“Machine punched” does not exclude hand punch- 
ing by means of the punch and mawl, or hand 
punching with the hammer to properly locate holes 
for fitting hips, etc., or obtaining suitable nailing 
surface. 


NGA lRORNT Agi ee elem ha Asst on OsCalele 1 iON 


4. Hips 
(a) All hips shall be laid to form “Saddle” Hips without metal 


underneath. 


5. Ridges 
(a) All ridges shall be laid to form “Saddle” Ridges. The nails 


of the combing slate shall pass through the joints of the slates below. 


6. Valleys 
(a) All valleys shall be laid to form “Closed” Valleys. 


7. Elastic Cement 


(a) Cement shali be an approved brand of waterproof elastic 
slaters’ cement colored to match as nearly as possible the general 
color of the slate. 


8. Nails 


(a) All slate shall be fastened with large-head slaters’ copper 
nails of sufficient lengths to adequately penetrate roof boarding. 
Care shall be taken to avoid exposing the nails on cornice, soffits, 
overhanging eaves, etc. 


9. Slating 

(a) The entire surface of all main and porch roofs, the roofs and 
sides of any dormer windows, if shown, and all other surfaces so 
indicated on the drawings, shall be covered with slate in a proper 
and watertight manner. 


(b) The slate shall project 2” at the eaves and 1” at all gable 
ends, and shall be laid in horizontal courses with the standard 3” 
headlap and each course shall break joints with the preceding one. 
Slates at the eaves or cornice line shall be doubled and canted by a 
wooden cant strip. 

(c) Slates overlapping sheet metal work shall have the nails so 
placed as to avoid puncturing the sheet metal. Exposed nails shal 
be permissible only in top courses where unavoidable. 

(d) Neatly fit slate around any pipes, ventilators, etc. 

(e) Nails shall not be driven in so far as to produce a strain on 
the slate. 

(f) Cover all exposed nail heads with elastic cement. Hip slates 
and ridge slates shall be laid in elastic cement spread thickly over 
unexposed surface of under courses of slate, nailed securely in place 
and pointed with elastic cement. 

(g) Build in and place all flashing pieces furnished by the sheet 
metal contractor and co-operate with him in doing the work of 
flashing. 

(h) On completion all slate must be sound, whole and clean, and 
the roof shall be left in every respect tight and a neat example of 
workmanship. 


If any other type of hip is desired, so state. 


If combed ridges, ridge rolls or cresting are de- 
sired, so state. 


If open valleys are desired, so state. “Round” 
or “Canoe” valleys may be used if desired but will 
add to the cost of the roof and are more frequently 
used with Graduated Roofs. For data see page 22; 
for Specifications see Standard Specification for a 
Graduated Slate Roof, page 59. 


Vertical surfaces may be iaid with 1” headlap. 
Specify cant strips of proper thickness under Car- 
pentry. Where cant strips occur above gutters, they 
should be placed before the metal. 


Standard Specification “T’’—Textural Slate Roof, 1925. 


a 


SEL eA CE ane ORs 


GRADUATED SLATE ROOFS 


The origin of the graduated roof forms an interesting bit of history. Their use in Europe dates back several cen- 
turies before the days of standardization, to the time when sufficient slate to cover the roof was extracted from the quarry 
by primitive methods without regard to definite size or established thicknesses. Doubtless the sizes made were those 
most convenient. Sent to the building, the slates were evidently sorted to some extent and hooked to roof lath by means 
of oak pegs. If an accident occurred to the roof, a messenger and cart would be dispatched to the nearest quarry for a 
“load of slate,” no attention probably being paid to size or thickness, and the roof was patched and repaired as well as 
the material might allow. As a result, a careful study of the roofs of former years discloses the fact that the charm 
of such roofs may be traced to mass, slope, the mellowing effect of age and weather, and the irregular texture, as a 
result of roughness of the surface and variations in length, width and size, all being more or less random. 

The graduated slate roof is the custom-made roof of the industry, and is therefore subject to individual characteris- 
tics and many variations to meet contingencies of design and conditions. 

In designing a roof of this type, the method of graduating will depend upon the size of the roof and its span, 
the “scale” of the building upon which it is used, and the general effect desired. A properly designed graduated roof 
should show no decided or noticeable break between the various thicknesses, sizes, etc. An agreeable and harmonious 
result can only be obtained by care in design and laying and the selection of the correct colors, sizes and texture. The 
interpretation of the design of such roofs is so much a matter of experience and good judgment that certain producers 
who have made a specialty of this work should be consulted and their suggestions obtained as to how to obtain the 
architectural effects desired. 

For most cases a maximum thickness of 1” will be found entirely satisfactory and pleasing in effect. The approxi- 
mate thicknesses always obtainable are 3/16", 14”, 39”, 1%”, 34”, 1", 144” and 1144”. The maximum practical thickness 
which can be used is 2”, but this is rarely used except for unusual conditions. 

Once the architectural effect desired has been determined upon, the length of the roof slope and the resulting 
number of courses will determine the rate of decrease in thickness or the number of courses of any one thickness which 
can be used. The occasional introduction of slates of varying thicknesses in the same course in some roofs is regarded 
as a desirable feature and affords another method of influencing the irregular character of the surface. In general, 
the large, thick slates used near the eaves will occur in fewer courses than the thinner slates toward the ridge. 

In addition to the usual standard sizes, slates above 14” thick are produced in lengths up to 30”. The graduations 
in lengths generally range from 24” to 12”. The longest slates are used at the eaves and the length usually diminished 
with the thickness. Here, again, good design dictates the range of graduations in length for any particular roof. The 
variations in length will at once provide a graduation in exposure by using the standard 3” lap. To illustrate, a 
suitable range of lengths might be: 


Under Eave Course %%” thick 14” long No exposure 


First Course yi PE ae 101,” 
iL 14 3,” (74 ae ce 101,” (74 
2 Courses LU oie KTS ONE 
Y “se 1," (74 20” 66 81,” (14 
2 (14 30" oe 204 (74 81," (<4 
A (14 3” (<4 13” (14 TY” (14 
Py 74 yy,” (74 We” 74 614” 74 
a (14 1,” (14 4? (44 olf” (14 
3 (74 BAO (74 a (a4 olf,” (+4 
8 74 3/16” 66 De (74 Alf” 66 


Random widths should be used and so laid that the vertical joints of each course are broken and covered by the 
slate of the course above. The variation in widths also tends to add interest to the texture and prevents a mechanical 
effect. The effect can be further enhanced by mixing percentages of heavier or lighter slates in each course of a given 
thickness. 

In splitting the thick slate, a slightly roughened surface is obtained and the edges are more or less broken. The 
usual tendency is for the thinner slates to split cleaner and with greater evenness of surface. As a result, the slate 
toward the ridge are smoother in surface texture and should be selected for their roughness or at least sufficient used 
to avoid a flat, mechanical appearance in contrast with the heavier slates near the eaves. This is especially important 


98 


Nee el OSNG AS eee ee alia oo eOCC Ar I OuN 


since the ridge slate, being farther from the eye, will naturally tend to appear smoother and more even than those 
lower down the roof. 

In addition to the variations described above, the color possibilities should not be forgotten. With proper selection 
the roof can be gradually blended from light to dark. In general, a dark roof appears to better advantage than a 
light color. Great care should be used in blending light to dark so there will be no pronounced line of demarcation 
of different shades. 

Slates for graduated roofs may be had in all the natural slate colors, and many interesting effects may be obtained 
by the use of harmonious and contrasting colors laid at random. If not too “spotty,” the weathering and ageing will 
tie the colors together, blending into a unit of unrivaled character. 

Heavy slates require the best of nailing. Any slates over 34” in thickness and 20” in length should be machine 
punched for four nails each. The smaller and thinner slates may be punched for two holes. Use only the best grade 
of non-ferrous slaters’ nails with large heads and heavy gauge shafts of sufficient length to secure ample penetration 
into the supporting roof surface. 

A heavy grade of felt will provide a cushion for the slates and provide additional insulation value. It is recom- 
mended that felt weighing from 30 to 50 pounds per square be used. (See Roofing Felt, page 23.) 

It is decidedly unwise to use any but the best of flashing materials and workmanship on so fine a roof. 

The construction of slate hips, valleys and ridges has been fully covered under the laying of slate, pages 14 to 23, 
and a repetition of this description is unnecessary here. 

Rafters and their supporting members should be carefully proportioned to the load which they must sustain. 
Sheathing boards of 7” material are ordinarily sufficient. When unusually thick slates are used, 114” sheathing boards 


should be specified. 
STANDARD SPECIFICATION 


FOR A 
GRADUATED SLATE ROOF 
NOTES 
1. This specification used as here given will provide for a complete slate roof as follows: 
Felt—Saturated Asphalt, 30 lbs. per sq. Cement—Elastic Waterproof. 
Flashings—16 oz. copper. Ridges—Saddle. 
Hips—Saddle. Nails—Copper. 


Slate—34” to 14” thick, 24” to 12” long. 
2. The following must be written into the specification under paragraph: 
3-c Slate—Color. 
8-a Valleys—Type. 

3. It should be noted that metal work is not covered by this specification, as separate Standard Specifications for 
Sheet Metal Work are given on page 49. The specifications for Slate Roofing and sheet metal work are so arranged, 
however, that they may be handled separately or together to conform to variation in custom in different sections of 
the country. 

4. See also General Notes—All Specifications, Page 48. 


SHORT FORM SPECIFICATION 


Norte: In using the Short Form if optional paragraphs are desired, so state. 


1. Slate Roofing For standard and optional materials and methods, 
(a) Furnish all materials and labor and cover with slate all por- see the| following paragraphs tn the complete form. 

tions of the building shown, marked or indicated for slate; form all Paragraph 1—Guarantee 

slate hips, ridges and valleys, in accordance with Specification “G” Paragraph I—Samples and Layout 

for a Graduated Slate Roof, 1925, of the National Slate Association, pa esioes awe 

791 Drexel Building, Philadelphia, Pa. (Note: if hee sizes and thicknesses than those in 


specification “G” are desired, specify exception at 
end of this paragraph.) 
Paragraph 4—Hips 
Paragraph 5—Ridges 
Paragraph 7—Elastic Cement 
Paragraph 8—Nails 
(Continued on Page 60) Paragraph 9—Slating 


39 


Saleen eOrOei aS 


(b) The slate shall be ; Paragraph 3-c—Color of Slate 
(c) The valleys shall be 2 Paragraph 6—Valleys 


2. Sheet Metal Work 


If part of slate roofing contractor's work, quote 
here the Short Form for Sheet Metal Work on 
page 49. 


STANDARD SPECIFICATION “G” 


(Covering in detail all materials and labor in connection with a Graduated Slate Roof.) 


l. General and Guarantee 


(a) The General Conditions of the contract are hereby made a 
part of the contract and this contractor shall examine these General 
Conditions and thoroughly acquaint himself with all the require- 
ments therein contained. 

(b) The roofing contractor shall furnish samples of the slate he 
proposes to use. A layout showing graduations, courses and color 
distribution shall be prepared by the producer and submitted to the 
Architect for approval. 

(c) This contractor shall furnish all materials and labor in ac- 
cordance with the drawings and these specifications. 

(d) This contractor shall inspect all surfaces prepared for slating 
by other trades, point out to the proper authority all defects, and 
shall not proceed with the laying of felt, flashings or slate until the 
necessary corrections have been made. 

(e) Roofing shall be applied by workmen experienced in the 
applying of slate. 

(f) The roofing contractor shall furnish his own scaffold or rig- 
ging, or arrange with the general contractor for the use of scaffolds 
furnished by others. 

(g) A written guarantee shall be furnished that the materials are 
in strict accordance with these specifications, and that any and all 
repairs required on the roof due to defective materials or workman- 
ship furnished under this contract shall be made without cost to the 
owner, for a period of one year. 


2. Roofing Felt 


(a) On all boarding to be covered with slate, furnish and lay For additional data regarding roofing felt, see 
asphalt saturated rag felt, not less in weight than that commercially peer 
known as “30 pound” felt. 

(b) Felt shall be laid in horizontal layers with joints lapped 
toward eaves and at ends at least 2” and well secured along laps and 
at ends as necessary to properly hold the felt in place and protect 
the structure until covered by the slate. All felt shall be preserved 
unbroken, tight and whole. 

(c) The felt shall lap over all hips and ridges. 

(d) Felt shall be lapped 2” over the metal of any valleys or 
built-in gutters. 


3. Slate 

(a) Slate shall be in combination of thicknesses from 34” to 14”. Any desired range may be used, inserting the de- 

(b) Slates shall be random widths from 24” to 12” in length. sired thicknesses and lengths. 

(c) Color of slate shall be ——————————— State color or color mixture, permanent or weather- 

ing, and percentages of each desired. 

(d) All slate shall be hard, dense, sound rock, machine punched _ “Machine punched” does not a ae pee 
for two holes. Slates 34” and thicker, when 20” or more in length, oa ae ae Ha ls Dung Pie a ne eres. 
shall have four holes. All exposed corners shall be practically full property locatedheles dors pte bine) Ce ormolrare 
and no broken corners on covered ends which sacrifice nailing ing suitable nailing to the roof boards. 


strength or the laying of a watertight roof will be allowed. No 
broken or cracked slates shall be used. 


60 


Nese le OoNt As eet eA teh FACS SO C1 A Tole O N 


4. Hips 
(a) All hips shall be laid to form “Saddle” Hips without metal 


underneath. 
5. Ridges 

(a) All ridges shall be laid to form “Saddle” Ridges. The nails 
of the combing slate shall pass through the joints of the slates below. 


6. Valleys 
(a) All valleys shall be 


7. Elastic Cement 


(a) Cement shall be an approved brand of waterproof elastic 
slaters’ cement colored to match as nearly as possible the general 
color of the slate. 


8. Nails 


(a) All slate shall be fastened with large flat-head slaters’ copper 
nails of sufficient length to adequately penetrate nailing surface. 
Use four nails for slates 34” and thicker when 20” or more in length. 
Care should be taken to avoid exposing the nails on cornice, soffits, 
overhanging eaves, etc. 

(b) Nails securing slate must in no instance be driven through 


flashing. 


9. Slating 


(a) The entire surface of all main and porch roofs, the roofs and 
sides of any dormer windows, if shown, and all other surfaces so 
indicated on the drawings, shall be covered with slate in combina- 
tions of colors, sizes and thicknesses shown on approved layout 
drawing furnished by Slate Producer. 

(b) The slate shall project at the eaves and at all gable ends as 
directed, and shall be laid in horizontal courses with the standard 3” 
headlap, and each course shall break joints with the preceding one. 
Slates at the eaves or cornice line shall be doubled and canted so 
that the succeeding course will have flat contact. 


(c) Slates overlapping sheet metal work shall have the nails so 
placed as to avoid puncturing the sheet metal. Exposed nails shall 
be permissible only in top courses where unavoidable. 

(d) Neatly fit slate around any pipes, ventilators, etc. 

(e) Nails shall not be driven in so far as to produce a strain on 
the slate. 

(f) Cover all exposed nail heads with elastic cement. Hip slates 
and ridge slates shall be laid in elastic cement spread thickly over 
unexposed surface of under course of slate. 

(¢) Build in and place all flashing pieces furnished by the sheet 
metal contractor and co-operate with him in doing the work of 
flashing. 

(h) On completion all slate must be sound, whole and clean, and 


the roof shall be left in every respect tight and a neat example of 
workmanship. 


If any other type of hips is desired, so state. 


If combed ridges, ridge rolls or cresting are de- 
sired, so state. 


Insert necessary following paragraphs: 

1—Laid to form “Open” Valleys. 

2—Laid to form “Closed” Valleys. 

3—Of slate laid to radius. The slate shall be 
tapered, shouldered, securely nailed and shall be 4” 
longer than the slates used in the corresponding 
courses on the roof and laid to allow the tail 
coursings to line up. Proper copper flashing under 
each course. 


Vertical surfaces may be laid with a head lap 
ayy I 
Specify cant strips of proper thickness under 
Carpentry. 

Where cant strips occur above gutters, they should 
be placed before the metal. 

If other construction at eaves and gables is de- 
sired, this should be noted here. 


Standard Specification “G’’—Graduated Slate Roof, 1925 


6l 


Sele shee ReOLOsr ss 


FLAT SLATE ROOFS 


Serviceable and permanent flat roofs are readily obtained by the use of roofing slate. The durable and wearing 
qualities of slate for promenade roofs are familiar to all who have seen and used slate for walks or floors. Slate 


possesses an apparent roughness due to slight irregularities of the “quarry cleft” surface and variation of color which 
give the appearance of a rough texture without actually being rough or hard to walk upon. As a result, where the 
design demands a promenade having qualities of this nature in addition to long life, slate will be found admirable. 
Its flexibility of arrangement adds to its other desirable features and allows unlimited possibilities in design. 

Where the roof does not serve as a promenade, slate can be used also to advantage in place of the usual slag, 
gravel, slate chips or plastic slate covering of any built-up roof. 

The nature of the material is such that it affords maximum protection against injury to the waterproofing mem- 
brane proper. The shape and weight of the units assure their being retained in place as first laid. The waterproof 
and non-absorbent characteristics of slate make it highly desirable as a surfacing material. 


Slate 


While any size slates may be used, the following have been recommended by the Division of Simplified Practice, 
United States Department of Commerce, as being readily available, economical and satisfactory: 


Approximate thickness of slate pieces; in inches................ Commercial Standard, average or basic; 35". 


For promenade or extraordinary service: 14 and 3%. 


Dimensions of Slate Pieces; in Inches. 


6x 6 10 x 6 1DExa6 
6x 8 10x7 Dexa 
6x9 10x 8 11 Se 3 


For promenades the above or any size or shape required by the design may be employed. 

While the commercial standard slates may be used for ordinary flat roofs, it is recommended that the 14” thickness 
be used. For promenades it is advisable to use the 14” or thicker. The 3/16” slates afford ample wearing surface, but 
the 3%” will permit better bedding and remain more securely in place under traffic. Thicker slates may occasionally 
be required by unusual conditions or other than ordinary use. A leading manufacturer of built-up roofings recom- 
mends slates at least 34,” to 1” thick, with sawed edges. 

The slate should be ordered without punching or drilling. Slates less than 3/16” thick are dressed or trimmed 
square with usual chamfered roofing slate rough edges. Slates 14” and more may be either dressed or sawed edges if 
desired, although the latter is more expensive. When using Pennsylvania blue-grey slates for flat roofs clear stock 


should be specified. 
Imbedding the Slate 


There are several methods of imbedding the slate. Some roofers mop over the felt waterproofing with an elastic 
bedding compound of 60% pitch and 40% asphaltum. 

In Newport, R. I., a manufacturer and roofer specializing in built-up roofs recently found it necessary to vary 
this mixture or top mopping coat to give satisfactory service to 50% Coal Tar Roofing Pitch and 50% Trinidad 
Roofing Asphalt. Another roofer has used Trinidad Steep Roofing Asphalt successfully. 

A San Francisco roofer has found that all mastics made for other work would not answer for slate. The com- 
pound must cement the slate fast to the felt and yet not run in hot weather, nor crack in cold. It is poured on hot 
with a ladle and the slate pressed down into it firm so it fills joints solid. This concern then runs a cutter over joints 
to cut down surplus compound which extends above level and does not stick to surface of slates because they first 
apply a preparation thereon, so it is readily peeled off leaving the surface clean. 

In several localities no special methods are employed. The three, four or five plies of felt are laid as recom- 
mended by their manufacturers, or in accordance with method of waterproofing employed, and standard thickness 
roofing slate are placed with butt joints in the top mopping coat instead of slag, gravel or slate chips, or other usual 
surfacing material. Many such roofs have been in service for several years. One case is known where standard thick- 
ness slate flat roof on a recreation pier has been walked on, danced on, and given very hard usage. For such installa- 
tions of standard thickness slate, the metal legs of benches or chairs should be nailed to a wood strip in order to 
avoid damaging the joints or crushing through the slate edges and puncturing the waterproofing below. 

Many successful installations have been obtained through use of cold plastic material for bedding slate. As a 


62 


Nee ale OM Neg ee ele AD be Anoo or Or Gel Ayr 170. N 


rule, about 10% of Portland Cement mortar or hydrated lime is added to the plastic to give it the proper stiffness 
and rigidity. 

Another group recommending and using roofing slate for surfacing flat roofs claim only a plastic compound 
troweled on hot gives satisfactory bedding of slate if a plastic material is to be used. 

A concrete setting bed is also recommended for promenades. Concrete composed of one part Portland Cement 
and three parts of sand or medium-size gravel is laid over the waterproofing felt. The concrete 34” in thickness forms 
a setting bed to receive the slate. After imbedding the slates and leveling them, grout the joints full or fill them with 
mineral wax. Expansion joints at intervals of 15 feet in each direction with suitable filler should be provided over 
the roof area. 


W ater proofing 

The supporting roof surface should be waterproofed by the method found by the designer to be most satisfac- 
tory in accordance with locality. 

Where nailings may be necessary to hold felt in place, this should be done in such a way that the nails are cov- 
ered with at least two layers of felt. 

Metal flashings should be covered with one or two pieces of felt before the imbedding material is applied and 
the slate laid. 


Roof Foundation 

The supporting surface of the roof may be of wood or concrete. If of wood, the usual sheathing boards as de- 
scribed under sloping roofs may be used. For mill construction, use plank sheathing of proper thickness for the span 
or rafter spacing. Whether wood, concrete or other material is used for this purpose, it is important that the surface 
be fairly smooth and free from nails or other projections which might puncture the felt or wear through under traffic. 
The sheathing slab or filling under the waterproofing should be sloped to the roof drainage points so that any possible 
water getting under the waterproofing from seepage of coping wall joints, etc., may be readily carried off. 


Roof Slope. 

The slope for roofs of this type should not exceed 4” rise in 12” of run. Slopes of less than this amount are 
recommended. For most conditions, 44” or 34” per foot will be found ample and as little as 14” will be satisfactory. 
When the slope is less than 14” per foot, it is important to see that the surface is evenly maintained and hollow 
spots avoided. 


Weight of Roofing 
The weight of the roofing material above the roof slab or boards is given in the following tables: 
WEIGHT OF FLAT SLATE ROOF WITHOUT CONCRETE BEDDING SLAB 


Weight of Materials Total Weight Total Weight 
Materials per sq. (100 sq. ft.) per sq. (100 sq. ft.) pounds per sq. ft. 
Waterproofing (Weight varies, assumed here to be 150 lbs.).... 150 <r soe 
PUAUE Sate ee ial irs han fh aed a ts Oe earths ve 250 400 4.0 
UAE SS) ENTS acs ich lest oan bec aL keaeas SRE etc Ot ee cece are rae 335 485 4.85 
SUS LA EC CIR Re ne eM a tas ors Se Padicsecch a 2 Ente eae eee 500 650 6.5 
LYS? RE NIelire AG oes Aha Si Oy eR eT Oe ee Pe 675 825 8.25 
SYA? SU ET ION wh exh cca rer ances.) et atlas COURS n ts ects oo ene err aRer Sar ae 1,000 1,150 HES 
IAS Late Morte vert thre Monica We Be Ria che MA doviel uale el Sema eeametas 1,330 1,480 14.8 


WEIGHT OF FLAT SLATE ROOF WITH CONCRETE BEDDING SLAB 


Weight of Materials Total Weight Total Weight 
Materials per sq. (100 sq. ft.) per sq. (100 sq. ft.) pounds per sq. ft. 

Waterproofing (Weight varies, assumed here to be 150 Ibs.).... 150 

See COUCTELEL DCU Lee yee PO RN ris Se SiS Meee tk eee 750 Gar ee 
SEEMS LLC cere ene ti aM Vote Oia cs ealey src Sans Ghee: oiBes i Satna 6 A cae 250 1,150 11.50 
VRS ACCME RE Pee et ee ea anos har rac Mote ci heat, Sig Se STR 335 e235 NESS 
Sia! TN ENON ocho coatag Od ben GE bel OO aNO CISIe Ba One oe ote eee Re RIC ; 500 1,400 14.00 
MgO La Le lapes wate e ae eon PR eM Ly Ne ncaa rice uertacls, ark, Granekedar else. ¢ 675 IASC) 15t75 
SAY SI CUI, a lob Mal eR Oo GTS nee Gig C OE er a nee oe 1,000 1,900 19.00 
1 SU ET PS. 5 oar5 je, Bee cas Case CELE ptr RTE Aa eS DIED tas a oe ca 1,330 2,230 22.30 


Sy LEAT ES aRIOsOrr-<s 


FLAT SLATE ROOFS—SPECIFICATIONAL DATA 


There are many methods for laying built-up roofs. There are many more opinions as to the most satisfactory 
manner of imbedding the slate or tile on top of the built-up roof whether or not for promenade purposes. It has there- 
fore seemed best in this edition to present the experience and specification data of some successful flat roof projects 
where roofing slate has been used as the surfacing material. Information on the use of slate chips instead of gravel 
or furnace slag or plastic slate surfacing will be furnished on request by the Association. As this volume deals only 
with roofing slate units, such types of slate roofs are not discussed. Nor are those roofs where slate granules or 
laminated slate surfaced roll roofing or individual shingles described herein. A list of members furnishing crushed 
slate for such purposes can be furnished on request. 

Every architect, builder or owner and even roofers in different localities have found by experience one or another 
method of built-up roof construction more suitable. 

Possibly as an outgrowth of the Federal Specification Board for unified, simplified, practical government specifica- 
tions, and through closer co-operation of roofing contractors through associate membership in this organization, 
there may appear in later editions of this work a standard specification for placing roofing slate on flat roof surfaces. 
Any architect, builder or owner desiring the protection advantages of roofing slate for the waterproofing membrane of 
flat roofs can obtain a list of similar projects in their vicinity so as to inspect them if they so desire before writing their 
specifications. Flashings and complete drainage of all water falling on the roof area or from seepage around stone 
work, etc., at coping or other edges of waterproofing base or the finished roof surface are prime requisites for satis- 
factory service from any flat roof construction. As one expert well states it: 


“Flashings and counter flashings seem to be the source of the greatest trouble in connection with roofs of 
all kinds. A great many people who design the construction upon which roofs must be placed seem to give no 
consideration to the limitations to the different materials that are used. They do not realize that the changes in 
temperature and the frosts very materially effect flashings, etc., and I have often remarked that it is rather strange 
that so little progress has been made up to the present time in connection with roofs, which are probably one of 
the first things that man ever commenced to construct in connection with habitations.” 


Some details of proper flashing for slate flat roofs are shown on page 23 as adapted from Copper and Brass Re- 
search Association handbook on Flashings. With the development of real research by such associations and the 
National Slate Association, not only will progress be made regarding roofs but many of the avoidable troubles will 
be done away with if recommendations are followed. 

The following are typical specifications for flat slate roofs which may be helpful or suggestive for wording others. 
The National Slate Association particularly requests experience data under such specifications or any others which 
have secured satisfactory flat slate roofs, whether or not for promenade purposes, so that eventually its standard Speci- 
fication “I” may be evolved for such roofs by the Slate Industry. 

A roofing concern in New York City which has specialized with great success on flat slate roofs publishes this 
specification: 


Specifications for Flat Slate Roofs over Concrete or Board Construction 

“After the roof surfaces have been properly graded to the proper outlets by other contractors, coat this con- 
struction with a heavy coat of Pure Asphalt Bitumen Roofing Cement, applied hot, in which lay shingle fashion 
five (5) layers of Standard Roofing Felt sticking the entire width of the sheets with the above asphalt. 

“After sixteen (16) ounce copper or other metal base flashings have been set by Metal Contractor extending 
four inches (4”) on roof and nailed three inches (3”) on centers, connect these flashings to the five (5) ply water- 
proofing with one (1) strip of felt and hot asphalt. As a walking or wearing surface imbed in a heavy flowing 
coat of Pure Asphalt Bitumen Steep Roofing Cement 6” x 6” Best Quality Slate not less than 1/4,” thick. 

“P. S.—If this roofing is applied over boards, omit the first coating of asphalt and blind nail the back edges 
otitelt.7 


The reflecting pool basin of the Lincoln Memorial is waterproofed and lined with roofing slate. Regular built-up 
construction is used, and after bedding the slates in the top mopping coat, they were again mopped on top so that 
there really is a coating both above and below the slate. 

Excerpts from Specifications for New Roof on Treasury Building 
“The roof covering not otherwise specified or indicated shall consist of the following minimum plies or layers 


and amounts of materials: 


64 


INSAe lel NGAY omen Lele ASS 0.0 GCG TATOO N 


1 layer of sheathing paper per 100 square feet, 5 pounds. 

5 layers of roofing felt per 100 square feet, 75 pounds. 

4 layers of roofing cement per 100 square feet, 120 pounds. 

1 layer of bedding compound per 100 square feet, 75 pounds. 
1 layer of slate. 


“Where the roof covering is applied directly over concrete the sheathing paper shall be omitted and 5 layers 
of roofing cement will be required with a weight per 100 square feet of 150 pounds. 

“Bedding compound shall be thoroughly plastic when heated for application, and must be strongly adhesive, 
free from any tendency to brittleness or cracking, or stickiness or creeping under natural temperatures when in 
place, and be unaffected by the elements. The compound shall not run or creep on a slope of 444” to the foot at 
a temperature of 140° F. when tested on glass or a similar smooth surface, and shall not lose its elasticity at a 
temperature of 0° F. 

“Slate shall be sound, hard, of fairly uniform thickness, not less than 3/16” thick; with square-cut edges, and 
in sizes generally about 8” x 10”. Smaller sizes shall be used on curved surfaces as necessary. 

“The slate shall be solidly bedded in hot bedding compound with butted joints, and neatly fitted to all con- 
necting work. The slate shall be clean and dry when laid. The completed roof shall be smooth and regular, 
and free from cracked, broken or loose slate.” 


One roofing contractor associate member specializing on surfacing flat roofs writes: 


“We have applied several thousands of squares of flat slate roofs in the past twenty-five years. The usual 
procedure is first to lay a three, four or five ply tarred felt and pitch roof, laid according to the manufacturer’s 
specifications, and over this roofing imbed, in a mixture of 60% coal tar pitch and 40% Trinidad asphalt, Stand- 
ard Stock roofing slate. 

“After several years of experience we are firmly convinced that the most serviceable specification for a prom- 
enade deck should be the Standard Specification of any of the well-known built-up roofing manufacturers, sur- 
faced with sawed-edge slate slabs approximately 7%” thick, laid in cement mortar over the roofing specifications 
above referred to.” 


A concern specializing in the construction of mausoleums has used various materials for roofing flat surfaces. 
Finding that maintenance and repair expenses varied for all types of flat roofs a special investigation and research, 
costing from three to four thousand dollars, was undertaken. After investigating all roofs of their own construction 
as well as many flat roofs built by others it was found that one with slate surface was still intact and had required 
no upkeep or repairs after 10 years, even though it was found that many large stones had been thrown on the slate. 
Slate was adopted as standard for flat roof surfacing and the method used by the concern is outlined as follows: 


“The Slate Roof that was built some ten years ago, was built with the standard built-up roof construction. 

“The slate were imbedded in the top mopping coat instead of slag. We have used no special method. Our 
latest building has been built in the same manner, and since completed has been examined by a number of roof 
builders who pronounced it as a roof that excels any other roof construction.” 


There is another group, developing built-up roofs and asphalts for flat slate roofs, who have this to say: 


“The admixture of asbestos fibre to a soft asphalt is better practice than to harden the asphalt itself in the 
process of refining. A soft asphalt reinforced with asbestos fibre is still a soft, adhesive asphalt and retains its 
adhesive qualities despite the fact that it has been stabilized and reinforced with the fibre. For the particular pur- 
pose of serving as a bed for slate it can be still further improved by the admixture also of slate flour. The asbestos 
fibre reinforces it but the slate flour gives 
it body and makes it easier to handle on 
the job, the same way that mortar is 
easier to spread than a liquid pitch.” 


From the foregoing it will be seen that 
it is impossible at the present time to include 
here a recommended specification, or even 
suggested paragraphs, for a flat slate roof. 
The Association is collecting data continu- 
ously on this subject, and will be glad to 
furnish the latest available information to 


architects and contractors upon request, and 


experience will be welcomed. 


65 


TYPICAL USES OF ROOFING SLATE FOR FLAT SURFACES 


Usual Flat Slate Roof Mausoleum with Flat Slate Roof 


Standard Thickness Slate Promenade, Recreation Pier 


THE LINCOLN MEMORIAL 
Roofed with Square Thick Roofing Slate with Sawed Edges 


REFLECTING POOL 
Lined with Regular Roofing Slate 


Showing the Roofing 


Roof of Mausoleum 
Slate Lining 


Shown Above 


| REROOFING WITH 


N old Oriental rugs, rare oil painting or ageing houses 
ese we are consciously or unconsciously aware of 
the effect of time. The contrasting colors of the rug 
are softened, those in the painting slightly dimmed, and 
the house has been toned so that the materials blend as 
one. We would instantly resent the insertion of fresh, 
new colors in the rug or painting. Yet some people 
thoughtlessly reroof their houses with a roofing material 
which cannot help but be incongruous and unharmonious 
with its surroundings. The ageing exterior walls and the 
profuse foliage of the trees and vines call for the use 
of materials which quickly become a part of the compo- 
sition. 

Slate possesses qualities which make it at once suitable 
for reroofing any type of building. It is a product of 
nature, obtainable in neutral or colorful, permanent or 
weathering tones, which quickly assumes the characteris- 
tics of age, blends with the natural surroundings, or by 
proper selection will conform to any desired color 
scheme. Its texture meets the demands of any design. 
Its cost is only slightly more than the less permanent 
roofings. 


Slate, being a hard, dense stone,.is fireproof, storm- 
proof, permanent, and cannot warp or curl. Reroofing 
with slate settles the replacement problem for the last 
time and assures economy in maintenance and lowest 
insurance rates. 

A reasonably smooth under surface is essential to the 
proper laying of any roof covering. Where the old roof 
covering presents a fairly even surface or can readily be 
made so, the slate may be laid directly on top of it. This 
procedure has been common practice for years, produces 
satisfactory results, and the old roofing possesses some 
insulating value. 

For high-grade work, it is strongly recommended that 
the old roof covering be removed. This insures proper 
examination of roof construction, rafters, etc. It per- 
mits of moving shingle laths or roof boards to proper 
spacing for slate, renewing broken ones and nailing all 
solid. In sections where heat conservation and the keep- 
ing out of air is an advantage, it allows the filling in 
with new roof boards between the lath so that the under 
surface may be solidly sheathed, smoothed and covered 
with at least a 14-pound asphalt felt. Should a respon- 


Applying Slate Over the Old Roof 


SalbeA- IE 


REO2O2bes 


sible slate roofing contractor’s inspector recommend the 
removal of the old covering, the cost of this adds only a 
small amount to the entire cost of the new slate roof. 
For a slate roof of commercial standard thickness slate, 
roof construction conforming to good engineering prac- 
tice for roofs of lighter materials will usually be found 
This applies both for new construc- 
tion and for reroofing, and will be found discussed in 


adequately strong. 


detail on page 34. 

The reroofing data which follows was originally pub- 
lished by the National Slate Association under the title 
of “Hints to Roofers on Reroofing with Commercial 
Standard Slate.” Since much of the information therein 
must be considered by the architect in recommending a 
new roof covering in alteration work and by the owner 
in deciding on the type of roof, it is reprinted here in the 
hope it will prove of value. 


WHEN THE OLp Coverinc Is REMOVED 


The removal of the old covering has the advantage of 
exposing the sheathing or roof lath and permitting a 
thorough inspection. Any broken boards or lath should 
be replaced with new whole material and all loose boards 
should be securely nailed in place. Boards originally 
so laid that the joints were not broken over bearings 
should be taken out and replaced or short rafters or 
blocking cut in to act as a bearing. In localities where 
the saving of heat is essential and roof lath has been 
used, if the lathing is not to be removed, new boards 
should be used to fill the space between the old lath. 
Both should be of the same thickness to provide a reason- 
ably smooth surface. 

It is important to go over the roof and remove or 
drive “home” any projecting nails and cut down any 
warped or raised edges or ends of sheathing or lath. 
Before laying the felt, thoroughly sweep off the sheathing 
to remove all chips, blocks and loose nails. 


WHEN THE OLD CoveRING REMAINS 


Where the old roof covering is allowed to remain, see 
that any low spots or loosened areas are filled up and 
made secure. Where possible to do so, inspect the sheath- 
ing or lath from the under side and repair all broken 
or loosened boards. In ordering nails, make allowances 
for the thickness of the old roofing and use a nail of 
sufficient length to secure thorough penetration into the 
roof boarding. 

Note the width of the roof boards or lath spacing and 
order slate of proper length to secure a nailing which 
will avoid the joints. The following table will be useful 
in this connection: 


= 


68 


Spacing of Lath (c. to c.) Length of Slate 


10% inches 
916 inches 


24 inches 
22 inches 


8% inches 20 inches 
7% inches 18 inches 


HEAVIER RAFTERS ARE Not REQUIRED 


Rafters adequate for wooden shingle roof will be of 
sufficient strength for slate of commercial standard 


(3/16”) thickness. 


Laying Slate Over Old Roofing Material 


It will sometimes be found that the rafters of old 
buildings—and some not classed as old—while of ample 
strength to support the present roof covering, were not 
designed to carry the additional snow or wind load rec- 
ommended by present-day engineering practice or re- 
quired by the local building code. 

When existing roof appears to sag or gives indication 
that existing supports are not adequate for the present 
roof covering, it would be unwise to replace the old 
covering or cover with any new material without strength- 
ening the roof supports. 

To aid architects and owners in overcoming such con- 
ditions, we would be glad to advise methods or send blue 
prints of drawings which the Structural Service Bureau 
has prepared showing methods for strengthening roof 
construction. It rarely occurs that conditions are such 
that the entire roof construction must be removed and 
replaced with members of larger size or different arrange- 
ment. 


How a NortTHERN Roorer Lays SLATE Over SHINGLES 


“In regard to the over-shingles work, will say that it 
works out very satisfactorily. Occasionally I have a job 


ING lee) Nae Le 


See Awl heer Seo, ORCtIE Nal LLOTN 


which is badly cut up with hips, dormer windows, etc., 
which should be stripped, and I do that. But the average 
roof lays very nicely over shingles with slates 18” or 
longer, and valleys go in well over shingles. Short slates 
do not lay well over shingles, as the slate necessarily 
rests on the shingle butts and it should span at least two 
courses of the wood shingles. 

“I lay the American method entirely, and do over- 
shingles work for about 25% more than the cost of 
stripping and reroofing with wood shingles. A 6d nail 
is used, which goes through the old shingles and into the 


roof boards. I also punch four holes in the slate instead 
of only two, as sometimes we don’t get good nailing and 
have to use the other pair of holes.” 

Another roofer, who has made a specialty of over- 
shingle work secures better results where the old surface 
is more or less uneven, with slates 12” and 14” long. He 
says, “They lay well and fit the contours much better 
than the larger sizes and further they are less liable to 
breakage where carpenters, painters and others must use 
the roof.” The Association partial payment plan makes 
reroofing with slate conveniently financed. 


MAKING ADDITIONS OR ALTERATIONS TO SLATE ROOFS 


_ Once a slate roof is properly laid it will be permanent 
and require little or no upkeep or care. However, houses 
are sometimes enlarged or remodeled. In such cases it 
is often necessary to join a new and old roof or to re- 
move and alter sections of the existing roof. 

It is desirable and necessary that the altered or addi- 
tional roof match the existing one in both shade and 
texture. To obtain this result, it is advisable to secure 
slate of the same quality and color as the original slate. 
Slates from some quarries weather, that is, the color as 
first quarried will differ from the permanent shade re- 
sulting from a few months’ exposure to the weather. 
Other slates are permanent or unfading and do not mel- 
low on exposure but retain the original natural shades. 

To match slates that are unfading, requires unfading 
slate of the same shade or slate which will weather to the 
desired shades. If the slate on the roof has already 
weathered, it can be matched with unfading slate or with 
weathering slates which will mellow to the desired effect. 
Securing slate from the original quarry, reduces trouble 
about matching or colors. However, in many remodel- 
ing jobs, the slate has been on the roof for many years 
and no record of the quarry from which it came will be 
available. 

An experienced slate roofer can usually identify slate 
as to producing vein but in case of doubt samples may 
be submitted to the Association for classification. 

The best method of procedure is to remove small ad- 
joining sections and relay, mixing some new slate with 
the old. This will prevent a clear line of demarcation 
where the new work adjoins the old and the completed 
roof will at once present a satisfactory appearance. 

In minor alterations such as adding or removing 
a dormer, the old slate which is removed can be used 
again. In dormers and other projections, the lights and 
shadows will differ from those on an expanse of roof, 
making it easier to add new slate which will be unnoticed. 
For example, new slates could best be used on cheeks 


of a new dormer using old slates on other parts. Some 


69 


roofers buy up a number of old roofs from buildings 
which are being torn down and thus obtain old weathered 
slate in their yards which can be readily matched with 
the slate on the roof when minor alterations are made. 
However, due to unavoidable causes, slates are some- 
times broken on the roof. The broken slate can be re- 
paired by the Slate Roofer. The best method is to first 
remove the broken slate, cut the nails with a ripper and 
remove any remaining small pieces of slate. Insert new 
slate and nail this slate through the vertical joint of the 
slates in the overlying course approximately 5 inches 
from the head of the slate, or 2 inches below the tail of 
the second course of the slate above; over this nail insert 
a piece of copper approximately 3 inches in width by 
8 inches in length. The piece of copper should be in- 
serted under the course above, lengthwise, so that it will 
extend a couple of inches under the succeeding course, 


thus insuring a proper lap and protection throughout the 


This small 


exposed joint in which the nail is driven. 
piece of metal 
should be first bent 
slightly concave or 
convex which will 
insure its remaining 
tightly in place. 
When making al- 


terations to a slate 


roof, only respon- 
sible and experi- 
enced slate roofers 


should do the work. 
If other 
are required to use 
ladders or scaffolds 


on 


workmen 


slate roofs, 
should be 
used under the legs 
or uprights to dis- 
tribute the pressure. 


boards 


Sfp N 
iA NEW SLATE \N COPPER 


PROPER METHOD OF INSERTING 
A NEW SLATE 


noted By oi, Wish Nn Olea Cy eats 


MISCELLANEOUS METHODS OF LAYING SLATE 


f SLATE 
vay Ey 


f | 
xp 
ei “ & LATH 


fo 


SECTION 


ROOT INE We 


SECTION 


+4 ARAFTERS TT 


—— 


‘SHINGLE LATH\ 
t 


SECTION PLAN 


FOR EXPOSURE SUBTRACT 3 FROM 
LLNCTH OF SHINGLE AND TAKE 
HALF OF REMAINDER 


OPEN SLAT/ING 


FOR USE WHERE VENTILATION 1/5 DESIRABLE 


SS 


WEEN OSS dae NS 


TAPCLA LCT) ea RIC, 


ALSO ANOWN AS “HEXAGONAL” OR “DIAGONAL” 
Fook Slate sometimes /21/2° with Undereave Slate 171 8" 


70 


Three methods of laying slate 
which are less expensive than the 
standard types, are here illustrated 
as they are in more or less com- 
mon use in certain localities. 

When properly laid they seem 
to prove satisfactory for certain 
purposes and locations. 


Dutch Lap: 
Laid with regular slate 
on shingle lath or tight 
sheathing. 


Open Slating: 
This method is also espe- 
cially suitable for barns 
and other buildings or 
where ventilation is desir- 
able such as_ slaughter 
houses or in mild climates. 


French Method: 

The diagonal, French or 
Hexagon method of slating 
being less expensive than 
the standard American 
method, has appealed 
mostly to New England 
thrift. Many, many car- 
loads of Maine and Ver- 
mont roofing slates have 
been so laid in certain New 
England cities not only 
when reroofing with slate 
over old temporary roof 
coverings, but also on new 
roofs. When laying new 
roofs of this method in that 
section where heat conser- 
vation is a factor, thirty 
pound instead of fourteen 
pound asphalt saturated 
felt is first applied on 
solid roof deck of sheath- 
ing or roof boards. The 
two sizes shown in the last 
figure on this page, with 
their respective undereave 
slates, are usually fur- 
nished and stocked only by 
certain quarries. For 
greatest service as with 
standard slate roof, sufh- 
cient lap of approximately 
3 inches must be provided. 
The 14 inch by 14 inch size 
is used on houses or build- 
ings with large gables and 
sections, while the 12 inch 
by 12 inch are used on 
smaller ones. 


x voc 


7 
ba 


9 Wes 


A Wer Libqye t 


4 


HE history of slate is an excellent criterion of the 
| Peete of this material for roofing. In France, 
England and Wales can be found better evidences of the 
durability of slate for this purpose than in our own 
country, for there slate roofs have been used for cen- 
turies. 

One of the earliest references to this use of slate is the 
construction of the roof of the Saxon Chapel at Strat- 
ford-on-Avon, Wiltshire, England. This was built dur- 
ing the eighth century and after 1100 years of constant 
exposure to all kinds of climatic changes, it is still in 
good condition although covered with moss. 

Slates were used to cover old castles at Carnarvon and 
Conway in North Wales during the twelfth century. 


Typical Slate Roofed Railroad Station 


These slates were thick and rough, as the workers had 
little skill in splitting and trimming. Today modern 
architecture is asking craftsmen to reproduce the handi- 
work of these early workers on special treatment, rough 
and thick slate roofs. 

The first authentic reference in literature to slate 
quarrying is the mention of the Penrhyn quarries by a 
Welsh bard in 1570. In 1580 Sion Tudor addressed 
some verses to the Dean of Bangor, Rowland Jones, re- 
questing a shipload of slate. It is fitting that the intro- 
duction of the world to so vast an industry should have 
come through the agency of people of such importance 
as the Dean of the Church and a poet of distinction. 

During the next two hundred years little is known of 
the growth of the industry, but gradually from a local 
market about Penrhyn, it had grown to considerable im- 
portance by the end of the eighteenth century. Quarry 
methods were crude and transportation difficult until 
1850 when the growth of the Welsh slate industry be- 


wal 


came very rapid due to the extensions of railways and 
the resulting widening of the market, the growth of new 
towns, improvements in rural dwellings, removal of re- 
strictive tariff and increased foreign demand. 

In France the rapid development of the slate industry 
dates from about this same year (1850) and for nearly 
the same reasons. The quarrying of slate on the conti- 
nent had begun long before this, however, and at Angers, 
France, a famous modern slate mining center, a slate 
roofed castle built about the twelfth century is still 
standing. 

A recent use of slate in Europe which is of interest to 
all Americans is the roof of the library of the University 
of Louvain. The Library, which was destroyed by the 
Germans in 1914, is being reconstructed by funds con- 
tributed by the Schools, Colleges and Universities of the 
United States. The plans were drawn by American archi- 
tects and the work of construction is being done by an 
American firm. The roof will be of blue slate providing 
an excellent background for the elaborate carving which 
will embellish the central motive and balustrade of the 
facade. 


Early History in America 


In America probably the oldest slate quarry is in the 
Peach Bottom district at the Pennsylvania-Maryland line. 


ai 
aH Wa ae 


eee 


Suggesting a Picturesque Use of Slate Roof and Trim, Fifth 
Avenue, New York 


Se lA ISEROLOgres 


Regarding these quarries, Ferguson, writing in 1910, says 
that slates mined near Delta in 1734 were at the time of 
writing, 1910, still in use covering the seventh building 
on which they had been placed, showing no indication 
of change in color or deterioration in quality. 

In Virginia, the first quarry was opened about 1787 
to provide slate for the roof of the state capitol. Slate 
was first quarried in Georgia in 1850. From such begin- 
nings, slate quarrying grew and spread until it became an 
established industry. From the very first, Welsh slate 
workers had an important part in the development of 
slate quarrying in America. It is a matter of record that 
about 1877, one hundred and fifty skilled slate workers 
left Bethseda district in North Wales to work in Ameri- 
can quarries. Many years prior to that, however, at the 
very beginning of the industry, Welsh slate workers were 
employed as is indicated by the names of many places in 
the slate regions, as Pen Argyl and Bangor, in Pennsyl- 
vania, which were named after Welsh towns. 

To attempt to list here all the prominent structures in 
America which are protected by roofs of slate would be 
obviously impossible. The National Slate Association 
maintains a list of such buildings and will be glad to 
refer architects to work in their locality where the various 
types of slate roofs and other features may be examined. 


Foreign Slate Deposits 

In the British Isles, the Welsh slates, particularly, 
those of Carnarvonshire and Merionethshire, are the best 
known, though slates are also produced from Cornwall, 
England, from Argyle, Perth, and Dunbarton, Scotland, 
and from Tipperary and Cork Counties, Ireland. 


ee. 


Stable and Gate Lodge Roofs and Pigeon Runway All of 
Roofing Slate 


72 


Attractive Community Theatre, with Roof, Sidewalk and Lobby 
Floors of Slate 


The chief slate mines in France are in the Ardennes 
and the Angers Districts. Great quantities of slates have 
been taken from these regions and much of the product 
has been exported. Slates have been quarried in Bohemia 
and near Olmutz in what was formerly the Austrian Em- 
pire, and along the Valley of the Moselle and in West- 
phalia, Germany. : 

A limited production of slate has been noted from 
Norway, Portugal, India, Italy, New Zealand and Tas- 
mania. 

Some of these foreign slates like some American slates 
formerly quarried are not true slate in important min- 
eral constituents. The Association will gladly report on 
any specimen sent it. 


Geological and Chemical Formation 


The following definition of slate has been tentatively 
adopted by Committee D-16 on Slate of the American 
Society for Testing Materials. 

“Slate is a microgranular crystalline stone derived 
from argillaceous sediments by regional metamorphism, 
and is characterized by a perfect cleavage quite inde- 
pendent of original bedding, which has been induced by 
pressure within the earth. The essential mineral con- 
stituents of slate are white mica (chiefly sericite) and 
quartz. Secondary prominent constituents are black mica 
(biotite), chlorite and hematite. Minor accessory min- 
erals are carbonates, magnetite, apatite, clay, andalusite, 
barite, rutile, pyrite, graphite, feldspar, zircon, tourma- 
line and carbonaceous matter. Igneous slates, because of 
their rare occurrence and insignificant commercial im- 
portance, are excluded from this classification. 

“Slate for roofing purposes should contain not more 
than x percent of carbonates (calcium or calcium-mag- 
nesium carbonates? ). 

“Slate for electrical purposes should contain not more 
than x per cent of metallic oxides or carbon.” 

In the last two paragraphs the percentages are still 


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The National Slate Asso- 


ciation will be glad to advise regarding the suitability 


the subject of consideration. 


of the mineral constituents of any slate for a particular 
location. 


Origin of Slate 

These minerals constituting slate were deposited in 
bodies of water and erosion and deposition accounts 
Other 
materials may have been deposited over the clays, and the 
pressure of the superimposed material may have grad- 
ually united the clays in shale. Shale has been described 


for the different composition in successive beds. 


as “a laminated rock consisting essentially of clay, but 
it does not possess the splitting properties of slate.” 
Some of the beds of shale remain as such today, but 
many have been subjected to the intense pressure and 
high temperature of the crumpling and folding of the 
When this has been the case the shales 
have been transformed into slates. 


earth’s crust. 


A Slate Quarry 


This tremendous pressure changes the position of the 
mineral grains until they lie parallel and at a definite 
angle to the direction of pressure. The high tempera- 
ture is at the same time acting with the pressure tending 
to change the constituent minerals to new minerals, such 
as mica, quartz, chlorite, magnetite, graphite and others. 
The “slaty cleavage” or ease of splitting in one direction 
is the result of the parallel position of the mineral grains. 


The Mineral Constituents of Slate 

The table on page 75 shows the mineral constituents 
of slate and their important physical characteristics. 
A petrographic analysis of slates or any stone or rock 


74 


formation is the only true study to determine the min- 
eral constituents which are the real proof of the identity 
of any stone or its classification among natural rock 
formations. 

The table on page 73 shows the results of a quanti- 
tative chemical analysis of slates from various parts of 
the country. Chemical analysis figures are valuable for 
comparative purposes, but often misleading because the 
same elements may be contained in varying proportions 
in minerals of very different chemical and physical char- 
acteristics. 

The analysis of Pennsylvania hard-vein slate is given 
separately because it has been made since the table on 
page 73 was prepared. 


Moisture at 100° Centigrade ...... .048% 
DHHGCA assem eater neds os eee eee (SIO,) 61.27% 
KerrictOxid ches genera + ak ee eee (Fe.03) 5.94% 
Aluminum Oxid ee tener (AL,O3) 16.46% 
Manganous) Oxides a) eo ee ree (MnO) 044% 
Galcinmy Oxide eae ee (CaO) 2.76% 
IMacnestuni Oxide ae ane (MgO) 3.399% 
iPotassiurine Oxi cle meae ee (K,0) 3.73% 
SOc Oxi cat eerste eee (Na,O) 5.92% 
Total Sulphur as Sulpbur Trioxide. (SOs) 84% 
Totall@n, cacy das eo chacien eee 100.411% 


The Quarrying of Slate 

Slate is quarried by different methods depending upon 
the structure and bedding of the rock. 

In Pennsylvania, the deposits are in nearly vertical 
In the 
New York and Vermont slate area near Granville, the 
bedding dips at an angle 
ranging from 15° to 60°, 


beds, but curve back and forth at steep angles. 


the average being be- 
tween 40° and 45°. Here, 
the plan of 
different 


therefore, 
quarrying is 


from that in Pennsyl- 
vania. 

The vertical beds of 
Pennsylvania permit a 
small surface opening 


which can be worked to 
creat depth and operated 
for many years without 
the expense of 
ing the overburden. Where 
the beds are at an angle 


remov- 


it is necessary to “strip” 


or remove large quanti- 
ties of waste rock or earth. 


Separating Block from Floor 


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Sele AS SE nan gia 


The use of shafts or drifts in the mining of slate is 
resorted to only where the vein is narrow and vertical 
or nearly so. The active slate mines of this type are 
now confined to the Monson district of Maine. 

Here each mine demands a slightly different method of 
treatment, some sinking a shaft and working the roof of 


the drift to obtain the slate utilizing the waste to build 


Landing for Blocks from Quarry Cableways enroute 
to Mill 


up the floor. Others combine this method with that of 
sinking the drift floor, taking slate from the floor and 
working down the bed. 

In each, however, fullest advantage is taken of the 
seams, making these take the place of a channel cut wher- 
ever possible. 

Hand drills, machine drills and blasting are used 


A Modern Mill Shapes Roofing Slate 


76 


to some extent, depending upon the location of the 
bed. The use of channeling machines, run by steam or 
compressed air, which give a smooth surface and provide 
a means of obtaining regular rectangular blocks, is found 
in Pennsylvania quarries. 


After the block is cut by the channeling machine, it is 
necessary to separate it from the floor. Where seams do 
not occur, horizontal drill holes are projected at the 
floor of the bench parallel to the slaty cleavage. Black 
blasting powder exploded in small charges then makes a 
fracture, separating the mass from the floor. These 
large masses are subdivided into slabs by splitting along 
the cleavage plane and can then be hoisted to the surface 
largest and most up-to-date quarries gasoline engines 


From the cableways the blocks are placed on cars at 
the landing and drawn to the mill or shanty. At the 
largest and most up-to-date quarries gasoline engines 
draw the cars directly into the mill. Here 
the slabs are lifted by electric traveling cranes 
and placed on saw tables where they are 
sawed and later “skulped” into conve- 
nient size slabs for the slate splitter. 

The slate splitter, using a flexible 
chisel and wooden mallet, splits the 
slab first in the center and continues to 


subdivide it in the center un- 
til slate are obtained of the 
required thickness. The fi- 
nal pieces are then trimmed 


4 


to commercial size either on ay rene 
Splitting and Trimming 


a foot treadle machine or by Roonneislee 


a mechanical trimmer, and 

hauled to the storage yards and piled on edge, each pile 
being made up of slates of the same size. Slates are 
sometimes punched before piling; at other times just 


before shipment, and sometimes on the job. 


Roofing Slates on the Quarry “Bank” 


an os 


JSE OF 


1/71/a 


AC BER TIRE ESEYS FA. fA. 


NASMUCH, as architectural training and taste are 
| Faves with giant strides in the United States, 
every architect appreciates the help he is constantly re- 
ceiving from well digested and carefully standardized 
literature issued by well established and reliable associ- 
Not that he 
But he 
does want reliable information in concise form and new 
and fresh ideas to help him in the use of the various 


ations representing different industries. 
wants his work to be standardized—far from it. 


materials he must incorporate in his designs and specify. 
No more convincing evidence of this is to be found, 
than in turning the leaves of half a dozen publications, 
issued by as many associa- 
tions, each pleasingly setting 
forth in text and pictures, 
new and proper ways to use 
their respective products. 
The text is often a model 
of condensation and clear- 
ness, while the pictures fre- 
quently are as valuable and 
as beautifully presented as 
those in large and expensive 
volumes, that many archi- 
tects feel they cannot afford. 
That the slate industry is 
represented among these en- 
lightened industries, is grati- 
the 


knows 


fying, since average 


architect far less 
about the use of slate than 
about some other products 
that have long appealed to 
him because of their well- 
known architectural 
bilities. 

Now in this book, I am 
limited to the of 
roofing slate only, and, 
therefore, I think first of all of the finest and most 


famous slate roofs in the world—those of the stately 


possi- 


subject 


Chateaux in the valley of the Loire. Fortunately, through 
the kindness of Mrs. C. C. Zantzinger, whose husband is 
a well-known architect, | am able to reproduce on the 
next page, a photograph of Azey le Rideau, usually con- 
sidered the most well-bred of all the Chateaux of the 
Francois Premier period, a picture that not only shows 
the type of roof I wish to describe, but one having the 
charm of the accidental about it. 

To be sure, the Chateaux itself, is only suggested, but 
its impressive gate houses and stately gateway, set off 
by grand old trees, show off the roofs in the foreground 


In Germany, for centuries, builders have woven designs in 
slate that are a delight still to every beholder 


U7 


gleaming 


these 


magnificently. Please observe great 
surfaces, as tall as the elevations themselves, but though 
the roofs are large, it is interesting to note that the small- 
est size and the thinnest slates (indeed, the cheapest) 
have been purposely used in order to increase the scale 
of the roofs and to insure a fine, smooth elegance. It 
is the smoothness and the fine texture that makes them 
so distinguished. Note the hip-lines in particular, while 
the metal cresting has been treated with boldness in 
order to make the slate all the more delicate and refined 
in appearance. 

Turning next to a German illustration, it is interest- 
ing to note how slate has 
been used in this high roof as 
an edging, much like a piece 
of braid around the edge of 
a fashionable cutaway coat, 
and again how beautifully 
the slate have been woven in 
around each of the dormer 


Here 


tions and many 


windows. are sugges- 
new possi- 
bilities, for it is possible to 


use up all the small and 


irregular and _ inexpensive 
run-of-the-quarry slate for 
the field, and the more 


varied in color and texture, 
the better; and then large 
selected slate of one color 
only for the edges and the 
frames around the dormer 
windows. 

One illustration, page 79, 
shows thick roofing slate put 
to a totally novel use. We 
see it here, the rough side 
out, forming a most artistic 


and durable 


and it is easy to imagine the delicate blendings of pur- 


wainscoting ; 


ples, greens and blues that add a note of spice to the 
interesting roughness and grainings of such picturesque 
surfaces. 

The dozen attractive pencil sketches prepared by Mr. 
Mecaskey suggest a hundred caprices that the architect 
may indulge in, if he has the patience and enthusiasm 
to spice up his work with a few fragments of slate. Archi- 
tect Andrew Thomas, of New York, has done this fre- 
quently with most pleasing results, one of which Mr. 
Mecaskey shows in his last sketch on page 82. 

In the first illustration, with less than a dozen thick 
pieces of slate, he gives scale and distinction to the most 


poysinsurjsip Os sfoo. asay? Saynut IY? B4njxa] auf puv ssauyjooUs 
ay? SI J] “Sfoo4 asayi 07 aouDsa]0 aa1d sayIMaM ay] 07 sayou dar 40 snof AjUO pin] aqwzs azn fo dn apowu saovfans suupe]s was) 


neospry = | AOZW jo nvoyey’) 244 Oj 90UB TO [eus1oy 


78 


commonplace archway. In the next, he uses slate more 
boldly for a little shelf over a triple window, and 
thereby adds a note of refinement to the entire window. 
In another arch, he separates the local stone by indi- 
vidual slivers of slate, thereby making the arch sparkle, 
while in the fourth, he suggests how a rich front door 
mat effect may be produced by using slate on edge as a 
landing. 

His fertile mind has evolved a number of other illus- 
trations of similar uses of slate, which the reader can 
decipher for himself, though I cannot refrain from com- 
menting upon the happy combination of the curved edge 
of a great roof just slightly projecting beyond the face 
of the wall and then the eaves corbeled out to receive the 
over-hang by means of many layers of slate, all of 
which produces a change in scale that is altogether 
charming, when used 
informal and romantic 
structure, but which would 
be utterly out of place on 
the Chateaux 
Rideau. 

I am surprised, however, 
that he has not furnished 
one illustration showing the 
use of slate in garden stair- 
ways. Nothing adds more to 


on 


= 
an 


of Azey le 


79 


the rustic charm of a garden than steps and stairs built 
with treads not over 114” thick out of rough slate and 
with risers built up of slate not over 34” thick, with their 
joints well raked out. 

Also at the risk of going beyond the limitations of this 
subject, I wish to say that if a tablet with an inscription 
is to be built in a wall, there is no other material with 
so fine a grain that will take the most delicate lettering so 
well. In support of which, I need only point to the ceme- 
teries of New England, where one still sees countless old 
tombstones, sometimes 200 years old, on which the in- 
scriptions are as clear as the day on which they were cut. 

I understand Architect 
Blanchard used slate me- 
morial tablets as well as 
roof and blackboards for 
Rockville Centre School 


shown at lower right, page 


py, 
APD 
Se 


Slate Dampproofing 
Courses. 


81. Lower right, page 80, 


shows unusual wall cop- 
Has not the 
Association made a happy 
selection of roof  treat- 


ing of slate. 


SCALE 
© SIN. GIN, 9M. I2IN. 
ess ms 


Slate as a dampproofing course has been 
used for many years. The Building Code of 
the District of Columbia states as follows:— 
“A course of slate must be worked into all 
walls to the full width of the walls, two 
courses above the surface of the ground and 


ments to intrigue the de- 
signer with the possibili- 


ties of the use of roofing 
slate? 


an additional course above footings where 
there isa cellar or basement.” 


A 


— 


= 


A few suggestions of the possibilities, both decorative and protective, in the use of roofing slate at the 
command of the designer 


80 


As one approaches the great Bear Mountain Bridge over the Hudson the slate roofs of the two gate houses seem 

to blend into the natural stone and foliage colors and become an integral part of the whole charming scenic effect. 

The other pictures show variations in the treatment of the details of slate roofs by which architects have secured 
unusual and pleasing results 


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INDEX 
A Page Page 
Additions to Slate Roof ...... so: 3 ROIS CARO Dice PAR BO 69 Pricesnofeslatebie. sccete setters sc eines oe toe soneninnes 47 
FAlteratlonsito wolates OO mee cc tes oe ects aes eis wae eaters 69 Punchines Slates Nallatolesieeeeeeeeeee ere eere eee 13 
C a Q 
Cement, Elastic, Properties and Uses ...........-2--e00+e- 24, Quantities of Slate per SQUATE «10... eee eee eee eect eee nee 12 
Colorm™Nomenclaturesots clatemaciaes osc sitar eeiiee lise elton a Quarries, plate, Now -Bemgu Worked cats ccis sess cosa 0 10 
Conductors Pip eS irc a\aeltetereracapaetes cts ee. clatelore aie. 8) Suaie oy she sleeve Nets 42 Quarrying Areas, Map -....6.... 0.0 seececeeneeccnsetneeees 84 
Conductor Pipes, Simplified Sizes and Weights ............ 44 R 
Constructionn etal see ctrcttescke se oie oleae ek scolel occneyeses 40 : 
: oF Rafters Allowable: UnitsStresses’ s-eeeosc ee cece ee een. 35 
Cricketsworsoa dd leSmepcivers see Goo ee tees Nee Oe eee 33 Totton’ Sivcsee Ushio of bey eee ee a hare er 35-39 
E Rerootineswithpslatemntnc ek sie tierra ee cee cre 7 
Rid gesmrrte Sie enn re at ee eee os 15 
Eaves Sieilalsfe\(e'6) elle\\silel/sl/el st eFolinl elelle {sk ol-6) ellaiielioie es) lelieiis volie el,¢.16\ e10) el611e).01e)\e\\0),0 "1s ele 23 Ridge, Comb phy SANIT sue Sra ht es, Sonta“ SRRN yoni ee eet 17 
Haviesmlnoug henner ae ctacte eco e csicuslvicier ate rom ne eramiteeislters 42 Rideoe Meal 17 
Eaves Troughs, Simplified Sizes and Weights ............. 44 RN Oe PUP EO = ISIN RRO COSMET BS NS Org REC ARC 
Boe : Ridgeyoad les ae roe ree ie. oe ee ee ee EE 15 
Histimatinege la shin gsm acetates cee soe cae ee neers sort 33 : : 
: Z ae Ridge omriproadaless oe era ee ee he ar ae ee ee 17 
Estimating Slate Quantities and Costs ..................--. 46 Root Brand 
EXPOSURE yette-ciccs crete res. ok saa craceierais, averavevaisinye revs eiclsrsv eyecare ere 15 Deg Nero erare ne SSSR: WIC, NaNO Meeker 40 
RootaConstruction meres roc one ake rane Lee 34 
F RoofsGoveringsmWeightsmencn cee comer eo eee 34. 
SIERO OG «Lacie cause oie eee gece! 23 Roofsliath Geter ene one athe dese ss oe eee es 40 
; RoofeSlop emer cet ot Sa rahe ore ort creer iohs area 42 
Hel€sRoofing, Weights. ajo csc. obistecten emacs one eles’ eracls 23 Ractee ives ofl and Part 45 
Hireproolme Constractionied ss. 6.00 cere nee clo aeeineo coer oienier 4] AY Re ar gene aia akon Aaa a 
late lo ofs.. D escriptiomcre cc cca cs ieeceraro eye eas 0: < aro aside sites as 6 S 
French Method of) Laymyg, Slate... 2. 2.26204. a6 cee eons 70 Saddlespor-Gricketseas ca cece sei seo tirke ee. 33 
Lasting sy Ae mas oor tic otals a's a.s aie ir ein chaus lv ial cloie ois weajsisaieje\ci« 30 SHea@tni epee ee cee ee heer oe haere relia toca Anita Oe 40 
lashin ges Ca pms osiscchrs acim oe iexs Fc Ske ofusle viele oes 4.0 s76 apie teers 32 SlatesAdvantacesy Of esa a cis at eenioe hee nen 47 
Pikash ing Sic COppelemtrcre cts e.acsseseaeyccie eis te iat cere aisieace lo opr 27 Slates, American Roofing (Table) ........................ 8 
ee ene OCCA Con rion Gan aes ae Color Designation 
ashinss.1 Generals mie oa, store ose ahs s1shore else eisi el witve) 0 aisle ofeieie. + Where Quarried 
Ellastnan g.6cg Wea diane rece eee otis ons srol scat vere cellar sua ticker ate eVeye ajo: roe foveus 28 Brief Description 
[RUA CHE te ECE! ac Se Deg Ugr Oe Ao aac I crane ter pis 30 Slates Basics Colores oot eee es Sas koe sake eee ee 7 
eae etelie Details iene eer i tserks eoeyera ie eek mae Slate; Characteristicsm remanence cc or lenieess ise cones 6 
ASIN ES SLI a Morte secrete ict sola: «. sysie eaeiev share cholerae sisus (esas gear eres Slates Colormemrsne re ere eee oe ae eaten 7 
Pleasing soeZ In Cg ae acttepe re irsiers sie akocs 5 ramet Weralvas sleee a oevers suancte 28 SlatessGommercial Standard, anaes eee 10 
Slates Commercials Standarde wecoienocie cs nce aceon 11 
G Grades, defined by districts 
Gablestmrrtcise ete reer esuete's: suites Scale sietarelay slo's oletdde wis eke sive oe 23 Characteristics and Weights 
pelvanie aon Me tenet er te voxer hercte tote: cunectevoiceleteisgeteanrs aye eieter veuos nS Slate, Dimension Nomenclature ..................2..e005 13 
Sree WE sopacé sons upangndad00d0d505 0nd 0oDDO CDH D0DDK Slates: Estimating oc 2c. sinew cr aeyeeince es Aer Ssivsioe sie sani ne telns 46 
Graduated Roof, Description ....................0+eseeees 5 SlatesMoreteny Deposits of) saaccos ae ee ieee oe ee ieee es eee 72 
(Gutterswmct oy eitioe cle icoieinls duces clos sis scehicie ga er ctavnie neice 42 Slates: General: Datavon.- tari eo te oes achat akc 71 
H ae pee ta and Chemical Formation of .............. 72 
; Ates Grane eo. e/a vsscpey ove ares oye cote ol'dlaleh soins  aYararahelers, eravevrlalelavs 10 
Hips ifeivet eile) sie ),efene ele) mieliccieje «se a's 0 © 0.6010) see. sie. 0 9@ 6 ee) ciel ele.e sis! ¢ a e.0¢ 18 Sista: Histor 
- Wie sitar sy ts sci cter nee ies telece clein Oreo olovernlereieve eicle viele @ atatie {fal 
Hp Been 200 0 BEDS DOOD OOOO ODO GOSUS SOS OH OGIO SOSH COD Ste bs Slate, Mineral Constituents of ...................00000e0ee 74 
Wh. Nason 099 CHOC ATTA DC OMS SChboCoCO CODD oUnCaDO DOC Ody S 18 Slatew\VliscellancoussWsesmrr rer nite ne cerns 77-82 
Hin’ S ied © RA) OO RA ON aM a a Re ia a AO O-SD 12 Slate, Origin olwernccr tomer co erteer as cote ak inet ilo een 74 
Hiby CECE pio clot Gogo bpIRe IOC 0 OGRE nO SO CHO OLMO RIK Obe 5.0 Ot * Slate, Quantitative Chemical Analysis ..................... 73 
J Slate Standards Detailsatnc teu Coc te caceesenenoek 16, 19, 20 
SOL SIat oe Mere ee bel ee) 14 Slates Standards Dimensionsmeeneee actin nee ones 10 
po ntioe of Slate L Slates Wieicht per squarewasa. terse oe oe ce ects nt cee 13 
SnO Wa Guard aes ce eee eo Pakais si we nS GTS 44, 
Laying, Miscellaneous Methods of ..................--e00- 70 Doldergecs mace Moc eerate cledielo comin ae sete ee einke: nares 30 
HAVIN GES ate tmtcien et ptetcts eeclaics: Sara tik ote dines obtlantieisjne ome ites 14 Specificationspe cr cas arom ry kerco ate ate acre iercaire erate 48 
LLG O» “ahe-aeSiceoncahace ete eh Olas ROIS Epc ee eens IgE OIE TARR Re 15 Specificational Data, Flat Roof ...................0000000: 63 
betray, BITTE (eee aio clcts cocina Dera Sinise ee eran mec 70 Specification) Graduated | Roofeesninedose ce cae aici eee ee 58 
ea OT SME eae Pole eee Toe, Cite pope ea Na Ci Soke ana Sadat 42 Specification;, Sheets Metal ic notte oe etter carelsshe ee one 48 
Mere tningeRoas mye etic cars teree tote re in tetera peiaies 45 Specification, Standard Roof 2.55... s0c000002000.5500cess 52 
N Specification, Textural Roof ............... cee eee eens 59 
Spates is StandardelvoofeLescriptiony eae en iee ie ie eenie 5 
BUM Ol esi ete va ORS i esie cee Oa aie colo elon Meera aes 
ELEY come Eh ca oe aR eR a A, 14 os T 
Wailea PulleSize Ulustration 2... 004 0-c% ais sme eae ees eee 26 Textural Roof, Description .............-.-...e2eeeeeeeee 5 
INailsmilencthssanduGauges on... .0 css. chek emacs ccc 25 Moolst Slateris rice see ene te ic ays ee eee ee eats 24 
INailssaMaterials of crac sioiere. + 07 ore.8 sivsis oveioiens. one saya Sige neta ss ehornns 25 Types of Slate Roofs ............. 0... se ce eens eee eee eens > 
Nail cspala bLesmo fies, ote sess cect are org ccsvedouss stoke. ons Glslotehal cisco. creect tens 26 V 
O Wialleyisgirrscvcstccepaethe ete Sra roe cereale aicie the ciosiersreoteete opevlore 18 
Oo CUPOLA EOP dD NY Re ene ies: eS Foe 70 Malleys) Ganoer occ se oom ociiemicte Sine elec a sisal siere-osiniciors slat ereis 23 
Le sata Pp Walleye Closed ixas ows chats cseide ss sates Selese idee actions otters 22 
WValleyss Open tress ocies oe are aoe nice eretaie vege ising eechere nec uteyesreieks 18 
Pit” QUIS” Gago eiomolmocins Gc DOS ree Hrere Oey nas cee Innes 45 alleys) Round Sioa cic coe coalesce tis scene siseus et echt sets 22 
Possibilities in Use of Roofing Slate ...................05. 17 Valley; Round) Foundation: 20... 2.0 6s so ae oes ec cess eee 40 


83 


NATIONAL SLATE ASSOCIATION 
MEMBERS ARE RELIABLE SOURCES OF SUPPLY 


This publication, together with recent brochure on “Charm of Slate Floors 
and Walks” and other informative literature on slate, have been made possible 
only through the complete co-operation of the members of the Association. 


< Soweeen eves gO The officers of this Association desire to thank the active or quarry and 
mill members, a substantial majority of the slate industry, who have so gener- “\@\RaRAairigs 
ously contributed of their time and money to make these works available to the — 
public. These members have been imbued at all times with the idea that the 
Active Members public should benefit from a wider knowledge and use of slate and that slate Associate Members 
Leswnte for its many uses may be properly installed to give the service warranted by Insignia 
the inherent qualities of this natural stone. 


In the past, when roofing slates were produced by haphazard and rule of thumb methods, some slates may have 
found their way on to roofs which present-day operators influenced by results of scientific knowledge and technical 
investigations would not tolerate. This is the trend of times in all industries for better products and better service 
from products. The National Slate Association is striving to secure for all users of roofing slate the centuries of 
sheltering service and high salvage value that this stone will give. Membership in this organization is an evidence 
of desire and willingness on the part of any quarry to furnish only high-grade, properly selected slate. Users of 
roofing slate will do well to 
specify and insist that their 
requirements come from quar- 
ries of members. This is not 
said with any idea of restrict- 
ing competition for any new 


Me SERMONT/ | MAINE capital or active concerns, for 
' the development of quarries 
eee in the worthwhile deposits 
F . will be gladly welcomed and 
encouraged by the Association. 
Portland 
en To protect the public the 


10) Cees 
x ONTAR! Association stands ready at 
ae Z 
GlensF 


merle all times to identify and 
ees Syracuse e HAMPSHSY) classify any slate. Recently 
Le eet degta, 2 “MASS it has developed that some 
\\ stag Cs slates formerly quarried do 

not come up to present stand- 
f ee: a ards of members so _ that 
ie PEVANi Aes nee architects and owners will do 
& well to obtain a report from 

the Association on any slates 


5 
dew new sd) ¢ io submitted for aroof from other 
>: JERSEY 4 than quarries of members or 


Albany | 


Sete AS Easton (Ay ya FIVE ACTIVE ROOFING deposits not located in the five 
‘ : On SLATE QUARRYING AREAS distinct and active quarrying 
Py ae () maine areas of the United States. 
North Blanchard 2 ° 
p Monson Architects, builders and 
WER MOT one ay oR owners may be assured that 
Granville- NY. 5 ° . 
Middle Granville - 1 they will be dealing with 
h ©. . : . 
Pouliney, Vt responsible parties if they 
 Washingto ee aes obtain estimates and informa- 
~~ ttle, . . . . 
VIRGINIA © PENNSYLVANIA tion on their slate require- 
Bangor ments in their localities from 
po RL al associate members of the Na- 
Charlottesville : Wind Cay : tional Slate Association. Such 
Chapman Quarries : : 
PEACH BOTTOM slate distributors, roofing and 
. coach eben setting contractors are readily 
elta,Pa 5 A C5 
Lynchburg Cardiff, Md. identified by their member- 


ship insignia displayed on 
letterheads, bidding sheets, in- 
voices, advertising, etc., or at 
their offices. 


